Melting them in-game actually, but yes kinda. I haven't figured out a good way to do it in world gen without the excess of having castes for everything, and the magic stuff that I'm using wouldn't be used during world gen anyway (excepting if I added something like vampirism or lycanthropy) so fire wizards in world gen would still be hitting people with sticks and stuff.
As for wilderness heroes, I've only ever seen one town with a serious animal man population. Most towns might have one or two of a non-standard species and overall they're still going to be very rare. Yes, multiple identical creatures should appear to show up more often.
In my best guess, vampires and other cursed individuals survive about 50% of the time. In a world with only three possible curses, yours, and one vampire and one werebeast curse each, you should see a bunch of your curse wizard running around. But increase those numbers, and youre going to see bigger and bigger ratios of other curses to yours. You can duplicate your curse to get more of them compared to everything else, after all vanilla vampires are all identical currently.
But you can't guarantee there will be enough people getting cursed. It only happens in temples, only while the temple has not been destroyed, and I have no idea how or if you can control the ratio of historical figures that profane temples.