I've read those citations before.
All of the citations seem to address alteration or manufacture. None of them really address leaving the mags unchanged, but using a different caliber bullet.
Alteration, I think, is the big issue. If you alter too much, you MAKE a new mag. The second citations addresses using parts from one mag to make another, in a different caliber. There you clearly have parts from TWO different calibers put together. I wonder if the modified mag would work in the "other" gun?
The Gun Test article isn't much help. (I've subscribed for years, but am thinking about letting my subscription run out. I don't think they do their homework.)
I think Brownells now only has tubes for SVI, STI, and Para-Ordnance guns, so its a non-issue for me. (And I've got enough hi-caps for carry... IDPA only uses 10-rounders, or less.)
Using a .40 mag, in unaltered form, in a 9mm gun, however, is something I'm concerned about.