[Brion Toss]

Hi again,
It would be tough to damage the metal with too much heat; you have to get it extremely hot to do that. Are the upper terminals fixed in "turrets" in the mast? If so, they almost certainly screw together through the mast, so you have to get the rod at right angles to the stick to unscrew. Have you tried that? It seems unlikely that acetone or anything else will help, regardless of the terminal type.
But what are the tangs? If they're turrets, they're not suitable for Dyform, so you could just install conventional tangs a short distance below.
And Bob, I can't figure how to respond to your question separately, so I'll say here that Navtec had some amusing dismastings with Dyform backstays before they discovered the cause: unlike 1x19, both core and cover on Dyform are laid in the same direction, so under load the wire wants to unlay. And unlike with a turnbuckle (a thoroughly cottered one), there's nothing to stop its doing so; it continues to unlay until something gives.
Fair leads,
Brion Toss