Many games support multiple floppy drives, and so will access the disk based on its name rather than the drive it's in. These games might work if you create assigns for the names of the disks instead. But many games are hardcoded with the floppy code, and even reassigning DF0: won't work. As zipper said though, any device can be dismounted using the Assign command as follows:
Assign DF0: DISMOUNT
Years ago I wrote a simple program to read the directories in the drawer it's in and create assigns for each one. It was very simple, but did work for a good few games. I must dig it up...
