How to prevent changing a segment value when an Alias is being used?

Summary:

We are trying to figure out a way, that an alias could be used to enter some (not all segments) of the GL Code combination (when entering transactions), and when chosen, those segment values from the Alias would be frozen.   Meaning, they could not be changed unless the alias was changed (or deleted and re-entered).

We have tried looking at a forms personalization, however the page to enter the COA combination (with Alias) looks like it is not up-datable.   Has anyone had any success trying to accomplish the same thing? And if so, please met me know the steps you did.