Though it likely won't help your current run: in my experience, Self-Modified is best handled by disabling the template's migration rights and locking in growth on that particular planet. If the Self Modified pops are in specialist and Ruler positions, they won't auto-resettle away (without some drastic restructuring to make them unemployed), so the population will stay restricted to their planet, and never grow (because of the locked in growth).I like to sometimes play with min-maxing my pop local traits, making miners, reserchers, priests, etc. but with thet mod it's VERY annoyng (and resetllement is part of problem) that especialy feels bad in my last game, while I play Idyllic Bloom plantoids with Budding trait and fanatic spiritualist, so I not making any king of robots and must settle 10 pops on unhabbitable planets before I could turn them to Gaia world. And Self-modified just ruin gameplan =(
It's very annoying if you're egalitarian, though. But then, if you're egalitarian, you may as well just ignore the fact that they can't resettle and just count them as a regular pop.