licensing question

I am about to move my license files from a citrix server to another citrix server (installed on Windows 2003 server - although it doesn't make any difference but i didn't know where to post my question!).

In order to do this, I need to log in to www.mycitrix.com and then "return, activate and re-allocate" the licenses. It seems pretty simple to do but the thing is that since I'm not an expert I don't know how things work and I'm afraid that this might happen:

When I "return" the licenses by clicking the appropriate key in MyCitrix, and change the name of the license server to the name of the new server, then noone will be able to log in as a user in the old citrix server. Is this possible to happen? Can I just "return" and re-allocate the licenses and still be able to work on the old server with users logging in?

It is very important that I don't do something wrong with that because the new server will be in service in february and till the last day of january the old server must be in full use. however, I cannot wait to move the license files till the last day since I need to test things first before the new one is in total operation.

I would be VERY greatfull if you could help me with that issue!

Myrto