thanks for quick reply!
i converted tile map to an instance and it can be edited exactly how i wanted it to. i didn’t notice that option because it wasn’t mentioned in documentation, and “convert to instance” sounds like it is for improving performance. so problem solved 
i thought about using a material instance to change texture, but i never tried it, because i assumed sprite texture sampler was doing something magic behind scenes, and i thought switching it to a regular texture parameter might break it somehow, so its good to know thats an option. are there any downsides to using a regular texture parameter instead of a sprite texture sampler? if they are interchangeable, it makes me wonder why sprite texture samplers exist.
that source region edit mode solves many of those problems, but if i paint 20 new sprites onto a sprite sheet that i have already extracted sprites from, i would have to use “create sprite” 20 times, and move rectangles into place. maybe there could be a button in sprite editor that allows me to add new sprites by dragging out a rectangle, so i can quickly add many new sprites to a sheet. it could use an automatic naming convention, kinda like extraction dialog, but since it would be a tool inside sprite editor, instead of extraction dialog, it might be easier to add change.
thanks again for these features!