I took a look at your code, and I couldn't figure out a way to easily make the mod only effect one item room on a floor with two. I had gotten sick of resetting the game on the Ultra Hard challenge, waiting for Pyromaniac to show up again. I did want to have everything else stay vanilla, however. I tried setting the list of possible items to only include the one I wanted, but that just caused a hard game crash when loading the second item room. My suggestion is to include some way, at least through a hard-coded variable, to switch the mod to only effect a single item room.