I wanted to start tuning cars. Like change rims add spoilers and stickers and change textures.
How to add stickers? In texture files there is like tons of the same pic each one is smaller (in Photoshop). Do I have to edit all of them. Also when saving the nVidia plugin gave me error.
How to change body parts?

You need to use 3DS Max to change body parts.

With the stickers, where are you trying to put them?

I wanted to put my YouTube channel name on some body parts and glasses.
Also want to tint and remove tint. Also change light colors and tint lights.
I used a tutorial that David has on his channel

Well it all depends on how the mod was made. If the paint has been rendered, you can apply liveries easily, otherwise its going to need 3DS Max.