[Graphics] Other grass animations in FR?

I want to insert new grass animations, other than the normal one and the unused ones that would use the same animation format of the normal FR grass. Anyone know anything about this? If this helps, I'm hacking FR and have the JPANS patched.
An image to ilustrate what I'm saying:

It's as simple as changing the graphic/adjusting the palette

Uhm ... how can I do this during the game? A forest tile that has its own grass animation and things like this.