#1)As an application programmer you dont have to specify anyhing.
IMS transactions are registered during IMS system defenition by system programmer. I wil try to give a more specific and clear answer soon.
#2) When you promote the code in to an IMS region load modules will be loaded in to that regions load lib.At a time there will be only one copy of a load module in one region.Library name is specific to installations.I think its system programmers task to specify the libraries at IMS initalization.Last point i'm not sure.Please let me know if i'm wrong.