I recently salvaged a thoroughly badass old 36-hole GT bmx hub and am thinking of using it to build a new front wheel for my bike. However, it appears to have a 10mm axle, so it won't actually fit in the end of my fork. I know it would also require new cones and nuts, but is it doable to switch the hub over to a 9mm axle?

i just got over a similar predicament (see: trouble installing wheels). I took my wheels to a professional bicycle mechanic (one of the best in japan actually) and his apprentice filed down the axle bolts from 9mm to 8mm in less than 20 minutes for less than 30 dollars.

Is it a high-flange GT "superlace" hub? I had a pair of those that are probably still in my parents garage and I've considered digging them out a using building a pair of singlespeed wheels. The spoke holes on the hub were not all the same distance from the axle, so it required a number of differing spoke lengths. Those superlace hubs laced to a pair of chrome Araya 7x rims was the lightest and strongest BMX wheels I ever had. When I replaced my heavy Perigrine 48s with those wheels I was jumping higher and more radical than ever before!!!!!

The flange is fairly high, but I don't see any actual model name on it. All the spoke holes are the same distance from the axle. I'll post a picture of it later today.

Edit: Here's a photo of the hub in question.

New axle?

File it down, no need for a new part.