[Rivet] Invisible BSM partilces in Rivet

[Silvan Kuttimalai]

Dear Rivet Developers,

I've come across an issue in Rivet when analyzing events that contained 
BSM particles which are supposed to represent some dark matter 
candidate. In many UFO models such particles are assigned an arbitrary 
particle ID and Rivet's guesstimate whether or not this particle is 
visible often gives the 'wrong' answer. Is there any way to tell Rivet 
on-they-fly whether or not to treat a certain particle as invisible?

Many thanks,
Silvan