So you can only build Local Colonies, when playing as Successors, if you go the Native Administration line. And you can't build the maximum level of Local Colony if the settlement has a Metropolis (but you can if it is a Minor or regular Polis).
So my big brain plan is, build a Minor Polis in a settlement, switch the government to Native Administration, build the local colony all the way to the max, switch the government to Hellenic Government (probably for good), and upgrade the poleis to metropolis.
I am playing on doing this because I noticed many of my periphery regions have got mediocre colony recruitment (up to second level, third level is just siege weapons), but everywhere seems to have a pretty good Metropolis recruitment (and not even counting the bonuses. Does it work like that?