InventoryList.csv is in the main game folder. Right click on the game in the itch app, choose "Manage", then again "manage" for the game itself (not the docs) and open the game's folder. Make a backup of the file though :)
For the disk swap, the easiest thing is before you want to play the swap game, press 'Q' to save game, and then make a backup (using File > backup scenarios or Ctrl-S). The backups are stored in your C:\Users\[your name]\Saved Games\Deathlord Relorded\backups\
Then go into town or whatever, kill and destroy and steal and exit. Then go in the menu Emulator > Insert Disk into Drive 1, and insert the backed up scenario A disk. Do the same with Drive 2 and scenario B. Re-enter the town or dungeon, it'll have reverted. Right away, choose menu Emulator > Insert Scenario Disks (or Alt->). It will put your active scenario disks in there again automatically. And press 'Q' in-game to save the current (good) state of the town.