Nothing much you can put some cooler camos and stuff on guns in zombies or multiplayer and thats about it
if you want a whole pack just to see what it kinda looks like heres my pack if you want to use
https://forum.plutonium.pw/topic/32218/my-almost-complete-bo2-pack-new-update-usable-camos-for-all-guns-mp
But there are some servers that have mods in them which they may slightly or drastically change the game with what they add in it
Were getting custom maps for bo2 now like bo1 and waw
There is some scripts that add a little to zombies which i recommend these ones
https://forum.plutonium.pw/topic/38491/share-mystery-box-perks-in-bo3-aats-tranzit-fog-cw-trial-system-scripts
https://forum.plutonium.pw/topic/46428/release-zm-tranzit-enhanced
This one is a little different
https://forum.plutonium.pw/topic/44566/release-mp-zm-t6-omnimovement-plugin-for-multiplayer-and-zombies
But if you want something really cool in your zombies i recommend this mod which adds all the perks and all the guns across all bo2 zombies maps in every single map which makes it hella fun!
https://forum.plutonium.pw/topic/42656/release-zm-mod-zm_expanded-combining-zm_weapons-zm_perks-into-1-mod
And this one that came out
https://forum.plutonium.pw/topic/46387/cod-bo2-dlc5-port-to-pc
Also theres this pack which just came out and itll improve your performance just a little bit if your computer somehow is struggling
https://aalonso.fr/vanilla/