woah, i'm reading the comics again and damn, Frisk is so badass! But i also noticed the "don't step on the leaves" sign in the ruins, and i already know that Chara changed it on purpouse (i saw it before in another ask), but i'm curious to know: before this mess, was the underground "identical" (or at least similar, i guess?) to the underground we see in game, or is it different because of some event or something?
This comic is less of an alternate universe and more of a canon divergence. Therefore, yes: in this story, the Underground was identical to that in Undertale, with the one major change being that Chara does not die. This single change significantly impacts the course of the story.