Hi,

It wasn't as simple as just making the tag writable, but it wasn't too difficult to add this ability. I have just released ExifTool version 5.90 (available now from my web site) with this feature added.

I hope this helps.

There is a third place where the resolution is stored though -- in the JFIF APP0 segment. Hopefully this won't cause problems, but if it does let me know. ExifTool currently doesn't write to this segment, so adding this ability would be a bit more work, but still not too much of a bother.