So, I managed to get twin Morgans, so to speak, using the old method of copying the already recruited one, and changing the hex value to turn them into the opposite gendered one. However, even if it worked neatly, without getting my important items whipped out, as the original Morgan had some supports, the new one is a bit skewed: For starters, this F!Morgan appears to be married to Gerome, yet, when Gerome is checked up, he remains unmarried. There are also a few filled supports, but they seem to work only on F!Morgan's end, as she doesn't even appear in the support listings of the other units.
I ran into a similar issue when I added a duplicated and genderswapped M!Kana to my Fates file, but the Fates save editor allowed me to edit away the faulty, one-ended supports, and now it works just fine, so I was wondering if there would be a way to tweak that issue in Awakening.