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The more deluxe theater organs had pizzicato and/or sostenuto features. They were implemented in the electro-pneumatic relay and required extra pneumatic switches (one per note for each function). Because of all of that extra mechanism and wiring, these were expensive options. Sometimes they were couplers (so you could register stops that would then provide the "blip" of momentary sounding on top of your registration for that keyboard) and other times (as in Link theater organs) they affected all of the stops drawn on that manual.
The Atlantic City Midmer-Losh organ has pizzicato couplers and I can tell you that the relay rooms have rows of pneumatic switches to provide that function.
Another feature found in Atlantic City are bass and treble couplers. Lots more individual pneumatic switches provide those functions. The lowest (bass) or highest (treble) note of a chord would be coupled to another manual and its registration.
As noted by Toodles, today any of these functions can be part of an electronic organ relay and it is all done in firmware. My Britson/Johannus has bass and treble couplers. They are useful for pianists playing an organ in a church because you can play all of the notes of the hymn on one manual, just like a piano, and the organ automatically plays the lowest note on the pedal and the melody note on a manual with a louder/brighter registration.
Main: Allen RMWTHEA.3 with Rocky Mount piano, Allen 423-C + Gyro cabinet, Britson Opus OEM38, Saville Series IV Opus 209, Steinway AR Duo-Art, Mills Violano Virtuoso with MIDI, Moller Artiste organ roll player
Lower Level: Hammond 9812H with roll player, Gulbransen Rialto, Roland E-200, Vintage Moog
Shop: Mason&Hamlin AR Ampico piano, Allen ADC-5300-D with 18 speakers, 4 matching Allen tone cabinets (including 2 Gyros, but don't call me Gyro Gearloose!).