How do I add and delete units from a nation?

[Edi]

Seriously, RTFM with the modding manual already! The nation modding section.

From all that can be seen on the forums, you do not even try to find out anything for yourself, but expect all answers to be provided ready-made to you on a platter. And it's a new thread for everything, which clutters up the forums. You could post just one thread titled "My questions on modding" or something and then post all the questions there.

Everything that you need for this is in the modding manual and all the answers that you need for this particular question, every single one, are found in the nation modding section and specifically the unit list commands.