I'm still sticking with my opinion and Greg's view. (thanks for the support)
I understand what you're saying about 'intention' and all the rest, but you're taking a practice swing that takes a divot and you don't clean the club face ... knowing that by not cleaning the club face will reduce spin isn't in breach of the rules.
Just for interest sake, I checked with a friend of mine in South Africa who is an R&A rules official and does duty at official sanctioned events (I just asked the question BTW, I didn't mention it was my opinion). He is of the opinion that's it is not in breach of the rules ... he alikes it to going into a bunker and while you dig your feet in you get a feel of the sand. You're not 'testing' the sand while you dig your feet in, you are using information you get to your advantage and that is not in breach of the rules.
He carried on for a l-o-n-g while about 'application', 'foreign object' ... blah, blah, blah ... but at the end of the day, if he was asked for a ruling under the gun he'd stay with his opinion that it is not illegal to take a practice swing and not clean the club face, even if you know that it will reduce spin or alter the playing characteristics.