See it here.

https://github.com/AlabamaHit/Bama-EtG-Sprite-Tool/tree/main/SpriteEditor

For enter the gungeon. Right now it takes images and replaces them in temp folder named properly where you can copy over to your created character.
There will be errors I put no catches in it because it was a personal tool. It will be getting updated.

It does not resize the images.
Right now basically it takes a file you want to change (marine sprite say)
Also if you made all your own sprites and names are off or you want to change base player. This will make process fast.
Drop in the one you want say (r&d enemy) it puts the new picture in a foler Temp.
Then you just have to copy the new images over to folder. No more renaming.

More options will be added any input help is welcome.

Yes code is under done. It was for personal use so I didn't do it right just fast.