I've looked in to this a little more. I'm still a little confused by this proposal. So it looks like you want the ability to disable the staircase's solidity independent of the enemies - so you can stand on the staircase while enemies pass through it, or pass through it while enemies stand on it.
However I'm not sure actually how your suggested "disable collision filtering" action would work, and how that would solve this. The only "collision filtering" the platform behavior does is to filter out any disabled solids. If you disable that "filtering", then it will act like all solids are enabled. So then you will always go up the stairs, never through them.
So I think I kind of see what you want, but I don't really understand what your proposed action would actually do internally, and how that fixes this. My first thought would be to have a Platform action to say something like "disable solid for this instance only", which isn't anything to do with disabling filtering. Alternatively there could be something like the LOS behavior where you can optionally choose a custom object/family to be solids instead of just using the solid behavior, and then you'd have to have two sets of objects for player and enemy collisions, which could then be separately disabled.
Either way, the Platform behavior has some of the most complex code in the engine, so I doubt this will be straightforward.