I don't think there are any set "rules" for that mate.
In all honesty and the majority of players wanted to play a different map then you probably did the right thing in changing it for them.
You could have posted an admin message saying that you were only changing the map for a bit to suit the requests and changed it back when you left.
Remember that the server should be busy and stay busy. If by changing the map people stay on server then you're doing a good job. Remember YOU are the admin and not the regular player.
Regards,
Rob