Did you mean it should be possible to generate an as from the skoolkit files?
Yes, you can generate an assembler-friendly ASM file from the SkoolKit source files for MM or JSW. In fact, that's one of the main points of SkoolKit - you can use the same source files to generate both the HTML disassembly and an ASM file.
You will need to download SkoolKit - for which you'll also need Python, version 3.4 or later - and use skool2asm.py to convert jsw.skool into jsw.asm (for example):
skool2asm.py jsw.skool > jsw.asm
I've successfully tested the output of skool2asm.py with pasmo, SjASMPlus and z80asm (the assembler that comes with z88dk), but it might work with other assemblers too.
It's the instruction which merges a guardian's INK colour and BRIGHT value (Bits 0-2 and 6) with the PAPER colour (Bits 3-5) of its host cells.
No, there's particular reason to use XOR instead of OR here. As you've noted, there's no difference in the resulting value in the A register, and there's also no difference in the effect on the flags (which are not checked anyway).