Okay, I looked it up.
If you have more than 50 men, more healthy men than wounded men, and more than 2 prestige you can disband half your unit. If you have more than 50 men, more healthy men than wounded men, and more than 10 prestige, you can choose how many men to disband.
If you have more than 2 prestige, have played BM for more than 9 days, and aren't travelling, you can set your whole unit up as militia. If all the previous is true, you have more than 50 men, and more healthy men than wounded men, you can set up half your unit as militia. If all the previous is true, and you have more than 10 prestige, you can choose how many men to setup as militia.
