How frustrating! Steel is very elastic, right up to the point where it isn't!! I'm inclined to be a bit on the cautious side, the consequences can be severe.
I'd keep going, you're trying to break the bond, so I'd be working it back and forth on whatever limit you feel comfortable with, tighten it back up, loosen again, squirt some gas, tighten again.... Whatever you're using as a pin spanner, leverage is your friend, as long as it's securely in the EBB a long bar on it ought to help.
Good luck.