Hello David ,
The query at its first look appear to belong to other fora such as
Process Integration (PI) & SOA Middleware
If you have group like XI, PI or PO then you should take this up with them.
If a work around to be identified in PM itself, then a very easy way can be, transfer the readings to new Equipments through the Transfer facility available in Measuring Points (IK02). Means the Process control will be functioning as it is and the readings recorded on the Old equipments (fridges) will be reocrd on the corresponding new fridges with this setting. In this setting (IK02) you will be mentioning the Old Measuring point in the new Measuring point as a source of reading. (Transfer of...)
Good luck
KJogeswaraRao