How to change the year of Roman system's changing?

[Atilius]

I've been also wondering about this method, but the problem is that you need the new building in all the regions. If not the post-reform units will be recruitable only in Rome.

You're entirely correct MW. Once the proper date has passed, I've been thinking in terms of either: (1) creating this building in every settlement or (2) monitoring the ownership of each settlement with a campaign script and creating it only in Roman controlled settlements which didn't already have one. This new building would be a requirement for upgrading a Roman barracks to allow construction of the Marian reform units.

With no clear plan yet, I thought I'd just sketch the general idea.