Well Reimu's asking Yukari to do something which even violates her morality. A last warning before crossing a point of no return. If you can justify effectively mindraping someone for this reason where does Reimu go next? Hell this might just loop around again in a while. If this comes out then where does it stop. Does this make Reimu a miko or a monster?
Even so...To living organisms, tampering with its memories means tampering with its existence...That's something only a god can forgive...It's the equivalent of you remaking her to fit your own desire.Even if everything goes well, and the problem has been settled......I will look down on you with scorn forever.