Hello @afielden the techniques used for creating custom modules vs updating an exiting module are the same, business rules, form layouts, workflows, ui policies, etc. what you do depends on what behavior change you are trying to achieve.
Perhaps you mean, how you can make a copy of an existing module so you can change the copy and leave the original as is. I am not aware a way to do that.
hope that helps
--
Bala
please mark this as helpful or a solution as appropriate.
