I've cut down a blue HPL carbon boom so that it could fit my 8.5 sail.
Cutting down the boom was not a problem at all but the fitting of the double push pin was a bit more tricky. Drilling the wholes is not the deal but the diameter of the boom arms where slightly smaller and I had some not so fun time trimming it down.
The boom is now still in a good shape and does the job, the boom head is going strong and I've equipped it with the perfect MauiSail boom head.
The only down side is that the boom feels fairly big and the rig appeals heavier. That might be good for light wind but when it is getting to the limit (that is how it should be in slalom) it doesn't go very smooth.
Anyways, you can do it and the boom will do it's job, even thought that it might not be the perfect solution depending on the bend curve.