Google says pewter melts around 170-230 Celsius, which heat guns can do. Unfortunately, if you're heating the entire BA up to somewhere near that temp (without melting the whole thing), some of the details may start to soften too. Ideally you'd only heat up the portion you're trying to repose, but that's a very tiny area, and you're using a heat gun.
And I'm not a materials engineer, so I don't know the math on how much the strength changes as you approach the melting temp. I think you're better off just slowly, carefully bending the bits. For BA you're probably safe.