Every patch of the Special Edition matrices can be reached with the appropriate marking or text in the score.
However, if you want to use MIDI commands (keyswitches and Control changes), that's also possible. To be honest, I don't know why you would want to do that, but here is how anyway.
Keyswtiches:
~Nxx,64 followed shortly by ~Oxx,64
These are MIDI commands for Note on and Note off. xx stands for the MIDI number of the Keyswitch. (24=C1, 25=C#1, ...)
Control Changes:
~Cxx,yy
For example ~C1,127 would send value 127 for MIDI CC 1 (=Mod Wheel)
For further details on MIDI commands in Sibelius see the Sibelius manual chapter 4.15.
By the way. If you are using Sibelius 5.2, I strongly recommend updating to Sibelius 5.2.5, which solved some playback issues.
Best,
Andi
Vienna Symphonic Library