possible to copy a time machine back up ?

I've been using a portable hard drive for my time machine back up so that I can travel with it. Since I've now run out of space on it and I'm traveling less I want to just use my server as a time machine back up- I'm not anticipating any problems setting this up.

Apple care tells me that I cannot copy my old time machine file (the one on the portable hard drive) to any other drive if I want to free up my portable hard drive for other uses. In other words once your time machine file ends up on a disc it is forever to remain on this disc and thou shalt "forfeit" your old back ups if you want to use your drive/disc for something else in the future.

does this sound accurate- any tricks for actually saving this data when you outgrow your ol' time machine drive ?

Any/all feedback appreciated thanks !! Erica

 

Thanks for the info.