Are you trying to have the teams stacked to only so many per team?
If so, use mp_autoteambalance 0 to make sure no one is auto transferred.
mp_limitteams 0 so that you can stack each team to whatever limit you want.
Do a check, say every round end, on each team. If ct/t has too many players ( more than what you want the max to be ) then have the plugin transfer how many is needed.