luis said:
If you use a rune for cursing you can clean your soul with Surya or Raum, it has been said so many times. I don't know about using a rune backward as I never tried it. You are mixing up information, only if you use a Sanskrit mantra to curse then Surya or Raum will not work and this is why it has been advised to not use Sanskrit to curse because it will stick to your soul even if you clean.
It makes no difference if it's a sanskrit mantra or a rune. If you use it directly for black magick like you say here, the energies
will stick to you on a soul-level and cleaning this would be extremely difficult. On the ToZ it has never been mentioned or advised to use anything like this for black magick, precisely for this reason. The only black magick methods that have been publicly shared by the HPs, are the Aura Deathspell (which does not involve mantras), and the backwards vibration of the runes which is mentioned in an audio by Pythia
here, at 7:33 minutes.
For anyone interested, a quick summary on known (and safe) ways to do black magick can be found here: https://ancient-forums.com/viewtopic.php?f=3&t=24711&p=109945#p109945