You don't technically install over top of any mods from 7H. It's a memory injection tool, so it only pulls modded files out of the IRO and activates them in real time when the game calls for it. Your game files are left untouched during the whole process. So if you were to install Reunion, 7H would be injecting your activated mods over Reunion modified game files, which could cause issues. Animations are hard to say though. The amount of iterations people can choose for modding FF7 now are WAY too many for any individual to test, so users are gonna have to figure out specific things like this more on their own I think.