I did, You can only add, not subtract.
Be careful, I think I blew my stock headgasket years and years ago accidently adding 15 of advance across the board.. It was fine untill I boosted.. then it was not fine..
I had the best luck setting the base timing at 5, so the car would run, barely, and then added in +5 to all the cells.. Then pulled them back to 0 or basicly taking away up to 5 degrees at higher boost. Problem was, I never could get the fuel cut to go away with 550's and the lexus meter, the Emanage blue.. Even with the the hz clamped at 1450.. No dice, it would hit FC, especially when boosting in a higher gear, under load.. Almost instant fuel cut from that, and only at 10 or so psi..
Pulled my car apart, and still do not have it up and running yet.. Lost intrest in the Supra. (Bought a sport bike.)