Not really, just an understanding of the file formats and a hex editor. I've never tried doing anything with the layer data in the MLVL so I don't really know exactly how it works, but the gist of it is if you scroll to the end of the MLVL you'll see a bunch of 64-bit values with a lot of FFs in them. Those are bit flags for setting whether a layer is enabled by default on a new save file or not. So to turn on a layer, you'd have to figure out which one of them corresponds with the room you want (it's presumably in the same order as the rooms earlier in the file), then which bit corresponds to the layer you want. Then just flip it on by setting the bit to 1. Changing one bit's not a complicated edit, but you do need to be able to read the file to tell which one you need to change.
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