Fan ideas for your new MOD.

[Arjos]

You can recruit roman archers...
No legions in Roma is nice and all, but there was the Campvs Martivs just outside and during emergencies legionaries were posted where needed...
Also this idea gets easily overstretched in time, it evolved during the middle/late republic and actually Sulla outlawed any legion in the city...
That was during a time there wasn't any threat in the italian peninsula, except for Romani themselves...

Reforms are fine and the inability to retrain is more than justified: there were new people or completely different equipments used, so the training and arming processes were different...