Did Rome actually retrained their old armies or they simply raised new ones in the new fashion, maybe they changed equipments of their veterans? I am always interested with this question.

I also found the reforms for Rome to be no inconvenience at all, they did mess up my armies sometimes but no big deal. Besides, they should mess things up. I would imagine Camillian legions mixing with Polybian reinforcement to be historically accurate since come on they just strip their whole arsenal in 3 months??? Such reforms should be huge and would require considerable amount of time to carry out, a few years I think, so yeah I have nothing to complaint. If you don't want to recruit new armies then don't, simply reinforce them with new units, maybe forming a corp of veterans in those legions, or sending them as vanguards so your new units can be fresh and tidy.

Also, until someone do something to Rome 2, I'm not buying that mess.