Lawl sorry for not seeing this sooner.
It's been a long while since I've hacked follow-me, so my memory is rusty, but I believe that the JPANHack patch (which I used with my followme) has dynamic sprites already in it, and so you would go to, say, everywhere I put in Pikachu sprites, and edit their value to make them a dynamic sprite instead in the manner that JPAN's hack tells you; I don't remember it exactly, but you do it in advanced-map I'm pretty sure.
Then, you would want a script before you unhide your sprite to make it change to the sprite you want. I believe the JPANhack documentation also says how to change the sprite dynamically, I think it's a var + special but I don't remember perfectly.
Sorry my memory is so bad, hah.
I might do 3ds modding at some point, thanks for the advice, although I think my 3ds is a newer one so it probably is fairly updated, and I'm also a bit afraid of breaking it accidentally.