Produce troop units wrongly

You cannot disband units, the closest option you have is get them into a unwinnable battle to get them killed off.

That will mess up your stats so the best is to have it be part of your larger armies and make them helpful to you

1. suicide them

2. mix them into stacks

3. use them for some naval scouting/unexpected invasions (which would fall unter 1 i guess)

Killing off your own men is a shame bro.

Just use them the best you could