1. Literally a normal Any% Celeste run (but assist mode is on and you don't use it)

2. go Epilogue

3. Turn on 2 dashes in assist mode

(to not lose time turning it on)

4. Submit pie screen and run

Is this actually allowed or an unclosed loophole?

NG+ Rules: "Unlock the Epilogue with dashes set to 2 using assist mode from a new file."

since it specifies "unlock the epilogue," i would say no. and if there's a loophole, i'm pretty sure the rules would get updated.