MeshConvert - a mesh editor for the Spintires format (those in MeshCache or _m)
MeshConvert saves ST game meshes for different game versions.
But not all meshes can be converted correctly; it is preferable to use the original X-meshes (with the .x file extension).
Also, MeshConvert can be used to edit the mesh XML.

Usage:
With this program, you can convert vehicles from the 03.03.16 version, specifically cached mesh files, to MudRunner.
Important! Don’t forget to then distribute all texture and model files into the necessary folders (which should be created beforehand): meshes go into the _m folder, and textures into the _t folder, accordingly. And provided the vehicle config in classes/trucks is correct, taking into account the new requirements for wheels and steering response. Also, the correct config for the wheels themselves in classes/wheels. The vehicle will appear in the game, though without drive shafts, as mentioned by the user above. Difficult? Possibly for some. But those familiar with the subject will figure it out.
How to use: unpack the downloaded executable into any folder. Double-click it, and in the window that appears, at the very bottom above the Load and Save buttons, select the path to the desired model (vehicle, addon), open the mesh, then click Load, and after that Save. A file with the _converted suffix will appear next to the model in the folder. This will be the finished mesh. Delete the old one, remove the suffix from the filename. That’s it.
Thanks for the instructions: Denis Korolev.

Source: SPINTIRES HARDCORE group

For loading the game save, it is ABSOLUTELY essential to have dls_east & dls_north & dls_fr & dls_italy. (Scandinavia & Going East & France & Italy).
(To avoid problems with loading this game save for users who do not have any of these DLCs!!!).
The save is named “ETS 2” (NOT PERSONALIZED – and perfectly suitable for any user!!!).

Map: 100%.
All garages purchased and expanded to 5 slots. Headquarters – Berlin (Germany).
All dealerships unlocked.
All recruitment agencies unlocked.
Driver: Level 50 “Legend” (rating 10.0).
Hired drivers: all have a rating of 10.0! (Dismissed, if desired you can buy trucks and hire them back).
Mileage: 300,000
Money: 200,000,000
You can change the driver avatar, company logo, truck brand, and company name by clicking the "CHANGE" button (in the Euro Truck Simulator 2 café).

Gameplay and button settings – customize to your preference!!! Graphics settings – adjust according to your PC’s capabilities!!!

Game version: 1.30.

Installation: Place folder 4554532032 (from the downloaded archive) into Documents/Euro Truck Simulator 2/profiles.

Kind request: First load the game save (make sure it works) and only then you can add your favorite mods to the game!

For loading the game save, it is ABSOLUTELY essential to have dlc_arizona & dlc_nevada & dlc_nm. (Arizona & Nevada & New Mexico).
(To avoid problems with loading this game save for users who do not have any of the DLCs!!!)
The save is named “ATS” (NOT a personal name – and is perfectly suitable for any user!!!).

Map: 100%
All garages purchased and expanded to 5 slots. Headquarters - Los Angeles (California).
All dealerships are unlocked.
All recruitment agencies are unlocked.
Driver: Level 50 “Legend” (rating 10.0).
Hired drivers: rating 10.0 for all! (FIRED, you can buy trucks and hire them back if you wish).
Mileage: 68,000
Money: 200,000,000
You can change the driver avatar, company logo, truck brand, and company name by clicking the "CHANGE" button (in the American Truck Simulator café).

Gameplay and key settings – customize to your liking!!! Graphics settings – adjust according to your PC’s capabilities!!!

Game version: 1.29

Installation: Place folder 415453 (from the downloaded archive) into Documents/American Truck Simulator/profiles.

A kind request: Load the game save first (make sure it works) and only then you can add your favorite mods to the game!

A batch file made for convenience, so you don't have to constantly move files from folder to folder if you want to play with mods in multiplayer.

How it works:
1. Before launching the game, all files from the media and texturecache folders are moved to temporary folders
2. The game launches, the script waits 10 seconds for it to load successfully
3. Then the script continues and moves all files from the temporary folders back to the working ones

I recommend making backups of all your mods!

Installation and use: place the .bat file in the root folder of the game and run it exclusively from there, you can also create a shortcut separately and choose the icon from the game's .exe file

Composition:
Import-export plugins: Axe free max (max7-max-18), Xporter (max5-max16), kwxport (max9-max16).
Scripts: Trackmaker, Copitor, InteractiveRenamer, Drag & Drop Reference Images, Tyre Tire, Debris maker, SoulburnScriptsPack.
Texture work: PixPlant.
Sound: Nero WaveEditor Portable.
.X file viewer: DxViewer.

Spintires MudRunner Mod On — performs the same function as spmmm, namely enabling mods in the game + delayed mod loading, cache clearing, Media folder cleaning, Config.xml patching.

Place the file in the root folder of the game.
Run as administrator.
On the first launch, the following folders will be created: Media_mod, Media, and Config.xml will be patched.
Media_mod - this is where mod files should be placed.
If you already have files in the Media folder, they should be moved to the Media_mod folder, because after enabling mods, the original Media folder with all its contents will be renamed to Media_original and mods will become unavailable in the game.

To work in delayed mod launch mode, go to the settings section, then specify the game file and the delay time in seconds. The delay time is the time after which the Media_mod folder is renamed to Media and mods become available.

Why is delayed launch needed? In some cases, when adding third-party mods, in multiplayer mode you may see the message "files differ from the original," the server does not search and does not create a room. This problem is often solved by enabling mods after the game starts.

Program on the author's website

A mod for control freaks or just those who love order and putting everything in its place.
After installing the mod, clear the cache with mandatory deletion of the Config.xml file, but specifically in the CACHE, not in the game folder. The files in the cache that need to be deleted are shown in the third screenshot.
Additional folders for mods. Mods can be placed in any of the suggested folders, taking folder priority into account.
Separate folders are offered for each type of mod.
The folders have different priorities. This is done intentionally. The highest priority is given to the Media_test and Media_level_test folders so that when testing a new mod, any issues are immediately visible if they exist. Then I suggest moving the tested mod to the Media folder if you liked the mod and it has no issues. After media test and media level test, the priority goes to Media_deffolt; this folder is needed if you tinker with default trucks and addons. Next priority is the Media folder, where I place already verified and liked mods for permanent use. Then the priority goes to Media_level, which is slightly lower than Media, because maps sometimes have built-in trucks and to prevent them from overriding higher-priority mods, the maps have slightly lower priority. Next is the Media_trailers folder, for trailers, if you need it, of course. The lowest priority is the Media_tracked_vehicles folder, which is for tracked vehicles. Although it makes sense to test this equipment first by placing it in Media_test, even after successful testing I place all tracked vehicles in Media_tracked_vehicles because they are still the most prone to various bugs and issues, so this folder has the lowest priority. And all these folders, naturally, have higher priority than Media.zip.

The video for the mod, as friends said, is quite old news, but it shows how you can create the folders you need yourself.