Hey everyone !
I started to dev a webtool, which (I think) could interest some creators.
It's a simple spritesheet convertor 3 columns to 4 columns.
How to use : Upload your 3 columns spritesheet, and that's it !
https://entitiesconvertor.web.app/home
Actually, it's only a proof of concept, but it will evolve later.
PM me if you're facing an issue.