Two ways that the behaviors differ from built-in parameters (probably related):

• Cannot manually set a parameter as one of the added parameters (they only appear when checking the box)

• When deploying a train schedule without setting the parameter, instead of the parameter it becomes whatever item/signal the parameter originally substituted (e.g. if you created the blueprint by substituting iron plates for parameter A, it puts iron plates on the schedule)

I'm guessing they just need to be added to the list of signals?

Correction: The parameters don't work correctly in train schedules whether or not the parameter is set. So if you create the blueprint with the parameter substituting iron plates, then place the blueprint using the parameter as inserters... the train schedule still uses iron plates.

whoops. accidental double post

Maybe I'm not understanding correctly, but I'm having trouble reproducing your issues. (It's also possible things are also just behaving differently after the migration to 2.1).

• Cannot manually set a parameter as one of the added parameters (they only appear when checking the box)

I see all of the 36 parameters in the Unsorted tab when selecting a signal.

• When deploying a train schedule without setting the parameter, instead of the parameter it becomes whatever item/signal the parameter originally substituted (e.g. if you created the blueprint by substituting iron plates for parameter A, it puts iron plates on the schedule)

If I name a station [item=iron-plate], place a new train, add station [item=iron-plate] to the schedule, blueprint the train, set [item=iron-plate] as parameter A, and paste the blueprint with [item=inserter] as parameter A I see this reflected in the train schedule; the same behavior as with parameter 0.

Ah, I wasn't clear enough. For the train schedules it wasn't station names I was having problems with, but the "Item count" condition.

However it also sounds like things have changed with 2.1, so that may no longer be an issue either. I guess I'll find out when I switch to 2.1, which likely won't be for a while.