Can you not set the value before spawning the emitter?
Easiest thing to do is to drag from the pin of the emitter template, create a variable, expose it so you can modify it in level too.
I have parenting and ownership running on Niagara emitters that are only visible to a special camera for distance field capture, so it’s 100% achievable.
It did need a work around though, and I do not recall what that was.
Probably had to do with setting the owner of the particle to be the camera actor in charge of capturing.