I know that EVILCUTOFF is shorthand ("mask") for all of the hostile allegiances: ENEMY, EVILBUTGREEN, EVILBUTBLUE and so on. Anything that refers to EVILCUTOFF is going to apply to any of these. But I became curious whether EVILCUTOFF might work as an allegiance value in its own right. It turns out that it can. I edited xvarts from ENEMY to EVILCUTOFF and summoned them alongside of some ENEMY ogres. Effects that targeted EVILCUTOFF applied to both, but effects that targeted ENEMY only applied to the ogres. This may have some uses for grouping-excluding creatures, for example, if you wish to put a spell only on a portion of the monsters in an encounter without any outward changes in circle color or behavior, you can switch some of them to EVILCUTOFF and target ENEMY with your effect.
Masks for alignment, MASK_LAWFUL and so on, should work the same way, except there is no recording which of the lawful alignments the creatures were in before the change; but then, it can be a temporary change.
