Stephen, i browsed thru most all my '89 magazines and came up with quite a few interesting images of the '89 Aggressor with the same decals as yours in two different color combos. Here's my theory about the evolution of the Aggressor decals.
The Aggressor "prototype" was introduced in april '89 issue of BMX Plus! Inside Scoop titled "Great minds think alike" reference to Haro's brand new innovation the bash-Master prototype which was featured first time in march '89 issue of BMX Plus.
Quote from BMX Plus! Inside Scoop april '89:"The GT bike name is still undecided, according to GT president Richard Long, but whatever it turns out to be, it should be available this spring as a frame and fork set."
Then came the actual GT Aggressor test review in june '89 issue of BMX Plus! featuring Woody itson, Trevor Hernandez and Ken Powers as test riders. Obviously the name was already decided but the bike, atleast the one in the test review, didn't have the name "Aggressor" written anywhere on it yet.
For the test bike they had just used the purple/pink/blue '89 GT "swirl" theme decals likely just to give the bike the distinctive "GT graphics look" for the review cause, my guess is, they didn't have the official Aggressor decals made just yet.
So Your '90 Aggressor has the mid-to-late '89 style decals that were produced for a while, but not long for very it seems. I'd say they are very rare, probably as rare as the '88 and '89 GT PFT decals.
In my '89 magazines i've seen images of the '89 Aggressor with those decals in two colour themes. White lettering for black '89 Aggressors and pink lettering for chrome '89 Aggressors.
Here the images. I pretty much scanned most every pic of the '89 Aggressor i could find, those with more less "clear view" of the decals in question, here goes.
First things first, here's the inside scoop "spy photo" of the prototype:
The first Aggressor test review, june '89.
Gary Pollak fence riding on, which i'm guessing is, the same bike from the test june '89 test review. BMX Plus august '89.
Now this is interesting. Joe Johnson on his blue '90 Aggressor with Pro Freestyle Tour
decals! Guess the hazard theme was already on during this photo shoot but the Aggressor decals didn't make it early enough to his bike for some reason.
...and this photo pretty much proves also that they were late with the '90 hazard decals.
From the cover of the GT 1990 Freestyle catalog, Joe Johnson and the '89 decals.