Some brainstorming notes, but using this in conjunction with @CT075 variable levels hack, you can create a trainee villager unit, for example, and allow them to use every promotion item to determine their T1 class.
Knight’s Crest → Knight
Orion’s Bolt → Archer
Coat of Arms → Soldier
Hero’s Crest → Mercenary
Guiding Ring → Mage
Elysian Whip → Pegasus Knight
Marauder Seal → Thief
Wyvern Flute → Dracoknight
This is what I had in mind for the FE1 remake. Dunno what to do with the actual Villager though in terms of weapons and such. FE2s use swords, 13’s use lances. We’d need to be able to drop weapons via promotion for this to actually pan out. But it’d be interesting to have ROM hackers handling the Villager better than FE13, for sure. There’s much potential.