Please help - this computer already associated with an apple id

We have 5 family members all using the same mac, each with their own login and password. Each person also has a seperate apple id/ itunes account - and we want to download all the music onto the hard drive.

When I go to do that for one of my daughters - it worked. Now I am trying to do the second one - and it says that

this computer is already associated with an Apple ID

You can download past purchases on this computer with just one Apple ID every 90 days. You cannot associate this computer with a different Apple ID for 83 days.

Any ideas...I am sure that this was developed for a good reason - but certainly not a family friendly policy where we are trying to upgrade and save everyone's stuff!

Any help or guidance is welcomed....