I mix and match into and out of established rat colonies and almost never have any problems. I move babies around or introduce new males and or females a lot and it doesn't seem to overly concer the rat colonies. Mice on the otherhand forget it never mess with the family group ... might as well feed them all off!
:Sorry to hear. From all that i have heard you not supossed to place a male or female into an established colony or your asking for trouble. Just curious as to why you didn't get another male and place them in a separate container and let them start a colony.