Leaf_Anbu

Hey was just wondering when making a mod pack. If you have to edit id's in mods then when it comes to updating these mods at a later date do the ids just revert to the original id or does it stay what you made it plus add any new id's in ? , if it overwrites any changes you have made then how do you prevent this ? or is it simply a case of everytime u update a mod u need to do all the id changes again ? . Thanks in advance for any help