TL;DR: Used "Install BCD" option and USB drive became "Basic" instead of "Removable".
I have a 64gb Sandisk flash drive, which was about 80% full. I wanted to install windows from it but didn't want to format it and lose data, so I googled if such a thing was possible, and came about an article saying to copy the .iso content onto flash drive and then use EasyBCD feature "Install BCD" to make it bootable.
I did this and clicked Yes in the dialog, but when booting from usb it gave an error. I decided to move the files to pc and then use Media Creation Tool to prepare the USB, but to my surprise it couldn't see the drive. I saw that it had changed from being "Removable" type to being "Basic",
so the windows doesn't see it as a flash drive anymore. I can read/write to it without a problem.
I reformatted, deleted partition and recreated it multiple times. I tried lexar bootit but I don't think it worked.
"Removable" is a feature of the USB firmware (a bit in the Inquiry command), which should not disappear.
Did you already try erasing the first few sectors of the disk entirely (with a shredder program or directly with a disk hex editor)?