I bought some used MFX last year and they also had the factory aluminum inserts glued in already.
I wanted to add brass inserts, but didn't want to chance degrading the shaft with heat.
I just swapped the tip end of the arrow to the nock end. You have to take off about 3/16" of the insert part of the plastic nock so they fit flush, but they still fit tight and work well.
My initial concern was that the aluminum insert in the rear of the arrow would change the spine, but that was not noticable.
The next new dozen I bought, I actually glued the aluminim inserts into the rear of the shafts just to keep the weight the same. Works well, does ad a little bit of weight.