is it just only cold planets?

Yes it will.

will this work on pre-existing universes?

@Bear It is hard to say.. I cannot think of a possible fix sadly. So yeah, you may just have to compromise there.

I would've thought as well, but I tried reinstalling it and it happened again, and it also happens with the other avali spawn increase mod (the one specifically for frackin planets). I have absolutely no idea what could cause it. My best guess is maybe it's a conflict with something else I have installed and a different mod is causing the problem but I can't venture a guess as to what it could be (I have several that have rail-related content that might be it) and can't safely uninstall anything else at the moment to check.
It doesn't appear to actually be all of my rails, either. Just the two longest ones. I couldn't even find cases of someone having the same thing happen outside of user error on designing the track. Thoroughly baffled, honestly. I will try to report back if I do manage to figure out what is causing this, though. In the meantime I'll just deal with having to go through a zillion planets for avali stuff, I guess!

@Bear I cannot see how that is even possible. You might have had another mod update that changed how rails work. Common avali literally only changes the commonality value of avali on select planets increasing your odds of avali spawn.

For some reason, adding this to my existing save made all my rail trams pop back into items and be unable to replaced onto the rails. I was able to get them working again by uninstalling it, at least.

la creaturas

you
you have done god's work
good job