[ASM & Hex] Object Structure

I have a some questions about the objects structure in FR.
First of all, the callback functions stored in the obj structure are just functions called every frame related to the object or are something more?
I tested some of them, the surf bubble one is just responsible for making the up-down movement of the sprite and nothing more, the player one is responsible to check the button press for movment, etc.
Other thing that I want to ask is about the template structure, some routines like the showpokemon one creates the template structure in the RAM for after building the hole object structure, the question that I have is: the template needs to stay there until the objects be deleted?
For example, if I change the template pointer in the object structure to FF FF FF FF how this will affect the object after it is already builded?
For the last, what is the difference in usage and results between "template_instanciate_forward_search" and "template_instanciate_reverse_search"?
Thanks for giving your time to help.

These are such bad names. Check out pokeemerald's sprite.h file and look for struct Sprite and struct SpriteTemplate. The functions you mentioned go by the names of CreateSprite and CreateSpriteAtEnd.