Yes, I think this will work.

For old mfe.c frontends, global variable set to "do it the new way" should be okey,
new experiments will have it the new way. Old experiments, will be forced to add a one-line definition
of this global variable (otherwise mfe.o will not link), at that time they get to chose "new way" or "old way".

For the new TMFE c++ frontend, this will work naturally when they create the Equipment Common object,
in the object constructor, you can see how it explicitly honors or overwrites the ODB common entries.

The TMFE frontend does not do a live "period", so there should be no issue with that.

Should I open a bitbucket issue "update TMFE frontend to new Equipment/Common scheme", to make sure
I do not forget about it?

K.O.