@lj_l – I think you handled your photo manipulation well for iNaturalist by saying what you did and by posting the original photo. I hope everyone who changes a photo does those things.
I also think you asked this question because you’re aware of the potential problems. For one thing, those of us who ID quickly may look at the first photo and make and ID if that seems clear, not noticing the rest. (I know I should look a little closer but, well, sometimes I don’t.) Also, important details may be lost or changed. For example, I’ve just been working on photos of a grass where hairs are important for identification. Sometimes I stare at the photo wondering if those hairs are present but in poor focus or just not there. It wouldn’t take much manipulation to accidentally add or remove a hair or two and thus change the ID I might make.