"Scope" of the project is a part of the proposal document (which is approved) and it list all the tickets selected for project
Well, yes, this is your way of working...
You are trying to freeze the scope by freezing items in it but you need first define the items list
My proposal is to fix the list, because scope is first list of items. It seems to me more accurate than "locking" tickets : with locking tickets, a ticket could be added in the scope...
what to do if estimates required updates?
In my proposal, treatment can be updated, and notes added ! This should cover this case.
another problem you should address - what about Agile: after iteration completed there can be changes
In agile, a version should just be a sprint : short version... The complete version cannot be defined at startup (as it is agile )
I think it much simpler to have an option to lock ticket description and links
I'm not sure it is the solution that will satify most situations. It is the simplest to implement but may be confusing for thoose who don't need it.