I have a multi volume hard drive and I use B: for one of my drives, as long as you don't change the boot volume, you shouldn't have a problem:
Go to Control Panel->Administrative Tools->Computer Management, and then go to storage in the left sidebar, expand it, and do disk management. from there, select a volume, and right click, choose change letter assignment.
This solution to your question should be most helpful, and by far the easiest