Hello,
pastoor:Does anyone know of a way of doing this in such a way that MPS is aware of it?
Couple ways exist. You can create mailbox for new users using MPS as usual, and then, behind MPS/HMC back delete mailbox and attach the old one. Then you will have to manually correct all user's attributes (e-mail address, AL/GAL membership, etc), Plus you have to make sure, that MPS will create new mailbox in the same mail store as deleted one.
Another way:
1. Create new mailbox as usual
2. Create dummy user (outside of HMC sandbox) and attach deleted mailbox to dummy user
3. Export attached mailbox to PST
4. Import PST to new user's mailbox (created on step #1)
4. delete dummy