I solved this as I did last time... I remembered exactly how I did it...
I could've gave just a few more minutes of thought and never have posted this question at all, but maybe it'll be helpful in the future anyways.
- Run diskpart (Win+R, "diskpart", Enter).
- List your volumes and reserved volumes by doing "list volume".
- Select the volume you want to change by doing "select volume ###", where "###" is the volume number seen in step 2.
- Assign a new letter by doing "assign LETTER=###", where "###" is the new letter.
In my case all of the volumes I wanted to change were all Type "Removable" and had a "No Media" Status with no other info, this indicates them all being reserved for USB.