[WindowsCentral.com]

You can manually assign permanent drive letters in Windows 10. This guide shows you how.

When you connect a new drive (a USB flash drive, optical drive, SD card or another type of storage devices) to your computer, Windows 10 automatically assigns a drive letter to identify the device and make it accessible. However, if you use multiple drives, you'll probably notice a new letter whenever you reconnect the same drive, which can be frustrating.
Fortunately, you can manually assign a permanent letter to any drive you connect using Windows 10 (excluding the C drive, of course). That's not only to stop the OS from assigning different letters. Windows 10 could also try to set a letter that's already in use, and you'll need to resolve the conflict. Or perhaps you simply want to assign drive letters in a way that makes more sense to you.
Whatever the reason, Windows 10 offers a few ways to manually assign permanent drive letters, as long as you connect the drive to the same computer and the letter is available.

Full story from the WindowsCentral blog...