The legacy plugin was written at a time when holidays were not yet supported by the OpenStudio SDK. I think they should work in the “Honeybee_Run Simulation” component but not the Legacy OpenStudio component.
The new LBT plugin (version 1.3 and above) uses the later versions of OpenStudio and has full support for holidays. So I would recommend switching to that if you need to use holidays.
The schedule objects in OpenStudio don’t support custom days so I’m sorry that the answer is “no for now.” If you badly need them, you can always manually edit the IDF and run it with the HB Run IDF component. Or you could write an EnerygPlus measure that adds the custom days.
But I’m sorry that this is at a level of detail that’s beyond what we can natively support.