There's another way of simulating choking of a cymbal in GP.
Make your crashed note (49, 52, 55, 57) normal dynamic (f, ff, fff, depending on your need), then right after it, put the same note with ppp dynamics. It will sound just fine, if "reverberated" a bit
It will also be easier to spot in Reaper's piano roll, you won't have to deal with volume CC, and you'll transfer it easier to the choke notes that are usually used by drum samplers (some use channel aftertouch for chokes, as well).
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