If you hardreset, you are just "re-applying" current ROM. So if you uploaded this one, you just re-apply this one (I mean this Beta). If you want to change back to previous, you have to upload it (=flash it) into your wings.
But the hard reset trick with the two soft buttons and then power button does nothing on my phone right now. I would like to keep the 6.1 ROM but just reset it to like it was originaly.
/Chrille