Edited IWAD in Slade after changing it to PWAD, and the change has affected ALL versions of the IWAD

[Xcel '99]

Alright, so... I was playing Final DOOM, I got to the Pharaoh level and noticed the key I needed was flagged as "Multiplayer". And, I didn't like the idea of having to just play with a separate PWAD that fixed the problem as I would need a new save to accommodate that. I opened TNT.wad in a Hex editor and changed "IWAD" to "PWAD", and then copied the edited data to TNT.wad, then saved it in Slade, opened it again in the Hex Editor to change it back to an IWAD, then saved the file. However, despite making an unedited backup in a different folder before doing this, the backup I have has also seemed to have retained the changes I made. I even tried reacquiring an untampered wad from Steam, but it comes with the changes still. Why is this? Chocolate DOOM also doesn't seem to register the changes to the yellow key, but does pickup the skybox change. 

[Xcel '99]

I should also mention running even the original wad I had through dosbox came up with "This version of DOOM has been modified" alert.

 

[Pure Hellspawn]

reinstall Final DOOM, and download the patch here

 

https://doomwiki.org/wiki/MAP31:_Pharaoh_(TNT:_Evilution)

 

or if you are in the yellow key area, you can just cheat to get it. you don't need the key to beat the level technically.