No, the drive letter is not static. If a drive was a train, the drive letter would be the platform number where the train arrives. Or if a drive was a plane, the drive letter would be the gate number.

Windows generally assigns the same drive letter to the same device, but if you want to, you could change drive letters randomly whenever you feel like it. The only thing windows needs is that every device has a different letter so that it can differentiate between them, but it doesn’t necessarily matter which has which letter.