I'm stuck on a level where I need to feed a bunch of items into mouths to get some doors to open, my only issue is I need a mantis idol to progress and I used it on a nook in the level below that turned it into a wand.

Is there any way I can edit my save and add the idol back into my inventory? Reloading unfortunately isn't an option as all my saves have been made after I used up the idol.

I never did that but I heard that All Seeing Eye (ASE) could do just that:

"- Inventory:
- Editing inventory makes the changes immediately.
- Click on a item slot to get its item index in the item array.
- If you want to set an item into an item slot, first check the item slot then select an item
from the item list and click "Set item".
- Almost every item in EOB games is unique so the game may crash if you create the same item
twice. Especially if you then move / throw the items around the map."
https://ase.zorbus.net/ase.txt

solved all my issues!

Thanks Cadaver, you saved me from having to start over. appreciate it!