When someone reach chuunin they get to choose between being an engineer(upgrade houses) or medic(heals)
if they decide to leave and choose the other one they should be able to keep their occupation lvl or get something like a demotion and lose some lvls.
This is for if you choose one and later feel like the other choose is more your style the work you up into the original occupation should not be erased.
Also if a large portion of you village is engineers and little medics you can switch in times when it is needed or convenient.
