From the author's README on Thunderstore

CJ (GTA: San Andreas)

Carl Johnson from Grand Theft Auto: San Andreas as a full-body costume for skate., running on ReSkate.

Find him under Apparel → Costumes.

What you get

The original San Andreas model with its own textures: white tank top, blue jeans, black sneakers.
Fitted to the skate. skeleton, so he uses the game's normal animations.

Known limitations

It is the low-poly PS2-era model with small textures, so he looks blocky and soft up close, as in the original game.
The hands are fixed, half-closed fists. Fingers do not move.
The face does not animate.

Install

Install from the MODS page of the ReSkate launcher, or extract the zip into its own folder inside Skate\Mods\.
Enable the mod and start the game through the launcher.
Open Apparel → Costumes and equip CJ.

Built for skate. Steam build 25414733.

Credits

Port by Ethan, made with Blender and ReSkate Studio. AI coding assistants were used for the conversion.
Carl Johnson and Grand Theft Auto: San Andreas belong to Rockstar Games / Take-Two Interactive.
Unofficial fan mod. Not affiliated with or endorsed by Rockstar Games, Take-Two Interactive, Electronic Arts, Full Circle or the ReSkate project.

Install CJ San Andreas

You need ReSkate and your own copy of skate. on Steam.

Open ReSkateLauncher.exe and go to MODS.
Search for CJ San Andreas and click install. The launcher also installs anything it depends on.
Press PLAY. In game, the MODS tab of the ReSkate menu (Insert) turns it on and off.

Or install it by hand: download the .zip and drop it on the launcher window, or unzip it into its own folder in Mods\ beside Skate.exe.

Maps show up in the ReSkate menu's level list. To join a server running a custom map, you need the same map installed. If the game won't load after installing, see known issues.

skatemods doesn't host or review this mod. The download comes straight from Thunderstore. Only install mods you trust, because scripts can run code.