Application Extension-Based Mods

I have looked at many tutorials and searched through the topics on this site to see if application extension-based mods can be added to either the server or client. I have found nothing. I have also tried various installments of the mod and nothing worked. Is it possible?

what type of mod’s you are installing?
so, if mod’s are like cars, you need is an addons mod, if are replacement, they didn’t work.
so,if are addon’s, and have unlockable contes,nedd to remove unlockable.

More like vehicle persistence and dealership mods