As long as you only have client side changes, it should be fine. So talking about texture changes mostly.
I suppose you could use a different weapon model (as long as you only change the bundledmesh, not the collisionmesh), but the animations most likely won't fit, so you'll end up with really weird results.
Animations, weapon tweaks (ammo changes, reload speeds and the likes), vehicle tweaks, etc. are all server side. You won't be able to join a server if you have those kind of changes.
If you want to do any modding, I'd stick with changing textures only.
