This 1.12.2 Forge mod adds a small config file that lets you control the frequency of zombie villages throughout the world.
In vanilla Minecraft, 1 out of every 50 villages generated is a zombie village. These generate with no doors and a population composed entirely of zombie villagers. This mod lets you either change the "1 in 50" chance to something like a "1 in 5" or even a "1 in 1" chance, and optionally to reverse the check (so, say, only 1 in 50 villages are not zombie villages).
Additionally, there is (in 1.1.0) an option to make zombie villagers not burn in daylight, as if they were a regular villager. This helps fix them from basically instantly despawning since they don't try to stay inside shade or anything (not smart...). This is off by default because it (unfortunately) affects all zombie villagers, since I can't tell if they were naturally generated in a village or not. (yet.)
Other than that, this mod doesn't do anything else to village frequency or size.
Tips:
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