For a simple-ish sprite edit, one could just edit the starting_loadouts mod which is included as an example mod with the game. Editing the sprites is a bit difficult because the player sprite is pretty big which requires a lot of edits. Likewise, if you change the rectangular size of the animation, you have to update the player.xml data which has all the data regarding the animations for the player. I think there is also a UV copy of the sprites you have to edit as well.
That being said, because of how the player.xml system works I think you could potentially change the size of the player to be any size if you are willing to edit all the sprites and the edit the player.xml.
Going beyond sprite edits, it gets a bit more complicated. There are lua hooks for stuff like EntityIngestMaterial( entity:int, material_type:number, amount:number ) which lets you do stuff like change the player sprite if they eat an amount of a material/materials. Still doing research on how all that works but don’t get your hopes up.
The player character has a lot of animations that one would have to edit in order to make a fat/bloated/inflated edit.