With Ohm meter you can check the alternator field terminal and see if you have 0 ohm short, or read some ohms. The rotor winding is the resistance in the field circuit. I am not sure how a ground in the regulator would damage the green wire as it would not force a high current on green wire. It would be 0 volts and low no output on alternator. To melt the green field wire it had to carry full voltage to ground to generate the current flow to melt insulation. Either rotor is shorted, the terminal insulator is broken/ground out, or the green wire had damage insulation that shorted to ground, but you said it was a tape wrapped wire, so probably not the issue.
The old style mechanical regulator is either on or off, iow full voltage or no voltage. A shorted green wire could very well burn up but as I stated those old style mechanical regulators usually have an internal fusible link that goes before that happens. However, there is no path to ground for the green wire inside the regulator, at least not normally, that would have caused the meltdown had that wire been back fed from the alternator.
Some measurements with an ohmmeter are needed here,
