Board Thread:Questions and Answers/@comment-27281654-20151227171647/@comment-27036118-20151230040004

Wow, alright, so a lot of rumors here.

Naming the fallen human "chara" has no special effects whatsoever, other than saying "The True Name" after entering it in at the very start. It's most likely just short for "character." It's a fanon name used because of the flavor text, and because the character has no official name.

And a more clear answer to the question: You cannot fight sans without doing a genocide run. However, after you beat Sans, you can reset your save data before finishing the route, and avoid the consequences of completing the run.