OK, I've just been messing around with this myself just to verify for you
Firstly, after not initially being able to find the command i eventually found it under:
ge_teamautobalance (that way round lol)
Secondly, even with that set to 0, when you kick the bots on your team, they automatically re-fill again and there doesn't seem to be any way to manually add a bot after the kick to the opposing team.
I was thinking along the lines of:
"kick <bot name>;ge_bot janus"
It kicked and then instantly replaced a bot, but it went onto MI6, my team.
I think in order to achieve what ahmedqman wants you'd need not only no autoteambalance, but also a way to manually specify a team when adding a bot. Don't know if that's possible?