1. For exch, all you should need to do is failover the virtual instance of exch to the node which doesn't need to have it's HBA card changed, basically make sure all resources are online on this node.
2. Then gracefully shutdown the server in question and replace the HBA card.
3. Dont forget to Zone i the new HBA card WWWN number so it can see the shared storage.
4. Make sure the driver/firmware at the same level and configure your MPIO etc...
5. The when all good, perform a failover/failoback and test exch.
Sukh