Hondo6

It is, and unless the frame's headtube is JIS and is also extremely thin that's likely the best long-term solution - IF you can find a local shop that has the tools and skills (or have the tools and skills to do the job yourself).

Unfortunately, today in many places finding a shop with the necessary tools and skills isn't that easy. I'm reasonably sure that the best shop I've found in my current local area no longer does this (or extends steerer threads, for that matter).

A viable alternative would be to ship (or take) the frame or fork to a remote shop - possibly a long distance away - that has the necessary skills and tools. But shipping forks and frames back and forth (or long road trips) can get pricey.

IMO, without a local shop available that can do the work it may be both easier and more economical to use a JIS headset - or some combination of parts from both types, if you're using a JIS fork in an ISO frame or vice-versa and can find headsets that use mutually compatible crown races. I believe Tange still offers some 1" headsets in both ISO and JIS, though finding those with JIS headtube inserts may now be getting a bit tricky. At least one Tange headset I've purchased recently specified as having a JIS (27mm) crown race in fact was also explicitly specified as having 30.2mm (ISO) headtube inserts. I needed at least the lower headtube race in 30.2mm (I had a spare upper) as well as a 27mm crown race, so for my purposes that particular "JIS" headset fit my needs perfectly.