Actually, I would suggest saving the change in a different location, one of the user banks, perhaps. You want to permanently alter the original tone. That would be a bit foolish, don''t you think? That is, unless of course, you want to go through the entire board and level the volume of every preset, seems a bit tedious to me. I think, in many ways, this is a fault in the device. One wouldn't think you would have to go through all the presets and adjust the volumes so that you can use them seamlessly and without killing your cat.
Even if you are simply doing this for a gig, and I would also advise doing it at gig volume, it would still be a tedious and monotonous task even to edit enough tones to fill the 5 FS's. Perhaps you could do it in banks. All the same, and I take what silverhead states--many of the louder tones are dependent upon the gain. Accordingly, if you lower the volume you will lose the nature of the tone. The only way I've found to avoid this is to adjust the volume of the amp I am actually playing, and that in itself isn't realistic in a live situation. I think, in some ways, the Firehawk FX has been sorely demonstrated. All the videos I've seen the player just soars through the effects as if there is no discrepancy in the volume, and we know this now not to be true. Retailers edit your videos, they are misleading.
Again, that said, I do see the Firehawk being a good tool for recording situations, but he whole idea that you use it live and just blow from one effect to another without any volume inconsistencies is bogus and far to tedious for anyone, or at least me, to consider.
Franklly, one might call it a bug, but I don't know that it can be fixed except to say it's a reason to using individual effects petals. So I don't know--in the end you always get what you pay for.
Good luck.