One would probably have to use Stalin-esque levels of oppression in order to successfully install such institutions in a lawless land. In the distant past, most rulers had no problems with ordering a few good massacres to keep the local population in line; it's much harder to get away with that today, although the leadership of countries like Syria and Sudan don't seem to be suffering very much

If the invading country can somehow manage to stay out of the public eye, they could oppress as much as they want. However, this is probably more random than anything, though if the invaders are "communist liberators" it might help - though their economic policies probably wouldn't be any good. All things considered, you're right if the conversion is by force.

Ideally, the conversion wouldn't be by force in the strong sense of the word - military police to come in and enforce some law and order, but otherwise live and let live. For this to work, the invaded country must not have any major cultural or ideological conflicts with their invaders, along with some other conditions that we don't know about. These conditions probably aren't in place for any given invader, but it remains a possibility.

Yes, the problem of developing good institutions is vexing. I doubt anyone knows much about how to do it.