Induced metamorphosis for pet trade seems like animal abuse to me, and I couldn't support that.
You're cutting the animal's life short, possibly killing it right then and there. For what reason ? Having a cool pet ? Meh (I'm also not a fan of breeding for aesthetics at the expense of health if it's avoidable, but that's a broad subject with lots of factors).
I don't know what's legal where you are, but I'm sure there are some cool creatures you can get your hands on.
Also, if no terrestrial salamanders are legal, this seems like exploiting an exception that could come back to bite everyone.