I also would keep the old overseers, just rewrite their missions.
Now this is slightly offtopic and might hijack the thread, still:
If the rewrite of such missions would be possible in one go, then I'd have an idea for a roleplay event: There could be a huge fair e.g. in Fairhaven. All the overseers would be wanting to go there for exchanging crafting ideas and recipes. The fair introduces a new fashion style, a new way of thinking, and thus the overseers would rethink their needs. When they return home, they'd have their missions changed. - Or change them over time after that fair. Homins might be required to protect individual overseers coming from faraway places. During the fair homins might be able to trade stuff in Fairhaven for special prices. Or they might be asked to help setup tents, or just help to pile up stuff for the overseers to do some demo crafting (e.g. digging requests).
Now this is slightly offtopic and might hijack the thread, still:
If the rewrite of such missions would be possible in one go, then I'd have an idea for a roleplay event: There could be a huge fair e.g. in Fairhaven. All the overseers would be wanting to go there for exchanging crafting ideas and recipes. The fair introduces a new fashion style, a new way of thinking, and thus the overseers would rethink their needs. When they return home, they'd have their missions changed. - Or change them over time after that fair. Homins might be required to protect individual overseers coming from faraway places. During the fair homins might be able to trade stuff in Fairhaven for special prices. Or they might be asked to help setup tents, or just help to pile up stuff for the overseers to do some demo crafting (e.g. digging requests).