I see you're already aware that the game has a 250 tile limit, and it would appear that Vanilla plus your mod use up nearly that whole field, so any mods that add several new tile types may be incompatible with this mod.
Here's my idea: change the name of the mod so that it lists at lower priority, making it so that tiles get removed from your mod before others--it'll be less noticeable that way because a lot of times X biome won't even be present on the game world, and when it is, the landfill texture still looks fine in its place.
I think higher letters have lower priority? If so, you could rename the mod zz-alien-biomes to put it at the end of the mod list. You might also be able to rename a few tiles similarly (ex. aa-mineral-grey-dirt) in order to make those tiles be considered first for removal. That way you can control which tiles are removed, and can select things that are uncommon, unimportant, or already look similar to landfill.
Just a thought, thought I'd share. I don't know if it'll work but I assume it would.
