Hmmm... I would send the fronts back and keep the rears
Are you racing/competing or is it just an HPDE? The whole heat cycle mumbo jumbo is true, you lose some grip as they wear down, but that doesn't necessarrilly make you slower or faster. In Spec Miata, I know MeatHead from MeatHead Racing likes to buy USED Toyos because he is actually faster on them.
I buy my tires full tread because I drive on them till I see the fabric cords poking through. The "Cycled" tire is still grippier than a normal all season street tire (or even summer tire). Since I am doing only HPDEs, I can't see throwing away some good rubber that I could be scrubbing off doing laps.
Sorry, off the soap box now...
To answer your question, I personally don't think you will notice a difference. the shaved fronts may grip a little better (maybe creating a tiny bit more over stear) but my bet is that it will all even out/you will get used to it by the end of the weekend.
Hell, the rate we go through rears compaired to fronts, you may go through the set as a whole evenly this way.
My vote:
Use up the A048 tires till you are PAST the wear bars, then take the R888 out for fun.