oh i did not see your post so i gave this a shot as well. below is some monkey code which caches MSB (instead of LSB) and triggers NRPN param change handling when LSB is received (instead of MSB). the code trashes D4 though to fit in.
; jump table entry for NPRN_LSB
; needs a tweak because NRPN_MSB routine is now shorter
;
4ff2 0x5130
; NRPN_MSB
;
511e btst.b 0x1, 0xccc3.w
5124 beq.w 0x500e
5128 move.b d0, 0xccc0.w
512c bra.w 0x500e
; NRPN_LSB
;
5130 btst.b 0x1, 0xccc3.w
5136 beq.w 0x500e
513a move.b 0xccc0.w, d4
513e move.b d0, 0xccc0.w ; just in case
5142 tst.b d4
5144 beq.w 0x514c
5148 bsr.w 0x3638 ; NRPN MSB == 1
514c bra.w 0x500e
5150 andi.w 0x7f, d0 ; NRPN MSB == 0
5154 movea.w d0, a6
5156 adda.w d0, a6
5158 movea.w 0x3654(a6), a6
515c jsr (a6)
515e bra.w 0x500e
wdyt? sorry to post untested code, don't have the machine. the controller code table should be as it is in original v1.2 OS (ie., 4fdb: 0x6362, and 4fd5: 0x0626)