HTC One M8 – Bootloop / TWRP unable to mount ‘/data’

So here’s a short story.
Ordered Unlocked HTC M8 from China. It arrived and worked but was missing the update option and was stuck on 4.4.4.
Found out the MID was Verizon’s 20000
Got Verizon image which worked, which locked the phones SIM card and branded everything Verizon.
I wanted to get the Developer version, so I changed my phones MID to 12000 and tried a few images. None worked, but now the phone is boot looped and nothing works.
Tried to load the Verizon image back on, but now I cannot because MID is wrong. Can’t change the MID because I only have access to fastboot and I need ADB.
Tried using TWRP to flash other images, but every ROM requires a format. The format fails TWRP unable to mount ‘/data’
The most promising one so far was SkyDragon‘s, but got "set_metadata_recursive: some changes failed" error on the Aroma installation.

I have literally spent the last week and a half stressing out and trying to get this phone working. I’ve never flashed a phone before and it’s been a complete ****.
If I can at least get the MID back to 20000 I can flash the Verizon image back on it and send it back to the seller.

I’ve tried googling the issue, but every single tutorial I’ve found is full of dead links or incompatible ROMs.
Phone is HTC M8. Phone is Unlocked. Fastboot works and I have TWRP recovery installed.
I am at my wits end. Please help.