Hello Lawrence,
On/off-type (latching/'stateful') MIDI switches, such as solenoid-actuated/illuminated draw-knobs/tabs would really need to be auto-detected to latching virtual switches (not to momentary pistons), in order to behave as one would want them (i.e. with their states matching the on/off state of the organs' virtual tremulants).
I don't have experience with the Steinmeyer sample set myself, but if it also makes latching switches available via the 'Organ settings | Stop/coupler/tremulant switches and pistons/buttons'' screen, then you could auto-detect them accordingly there (instead of needing to use its momentary pistons).