I actually quite like the idea of being able to choose whether to upgrade to Polybian era units or not. One of the things that always bugged me was having these elite (i.e. many chevron) units that all of a sudden can no longer be repaired nor upgraded to anything useful and thus just end up sitting around. Sure it might not be 100% realistic but then neither is not being able to change one unit type into its reformed version (but I guess I have CA to blame for that ;)

Right now I have most of my cities changed to Polybian barracks but only Capua remains pre-Polybian so that my units can be repaired there (and so that I can still recruit Samnites - any replies on why they disappeared in Polybian?)