I have found a way to make this work.
First though, Brian, Change Instrument when applied to only a single measure presumes you wish to remain there for the remainder of the score. You will need to add an additional Change Instrument to return back. Any change region of more than 1 measure and Finale will automatically add the change back into ScoreManager.
Now for the fun stuff, get some popcorn and a drink.
Using a blank or empty bank in Kontakt (rather than loading 1 instrument into a single midi channel load an empty bank) load in the pitched instrument or instruments you wish for that stave. This would be the best way to handle mallet changes as well by the way. To load the instruments into an empty slot in the bank, click and drag the instrument rather than double clicking. Double clicking will add the instrument into a new midi channel. What we are doing is assigning multiple instruments to a single channel. Each instrument is a separate patch. An example would be Marimba 1 is assigned to midi channel 8 so you load the empty bank , which can hold up to 127 different patches or instruments, and make sure it is set for playback on midi channel 8. Now navigate to the Marimba folder and open it and click and drag the synthetic soft marimba to slot 1 in the bank. Click and drag the medium mallet instrument to slot 2 and the hard mallet instrument to slot 3. Finally, navigate to the combo folder and click and drag the cymbal rack instrument to slot 4.
With this set up, you will use text expressions to do patch changes to switch from 1 instrument to another. All of them will only use 1 midi channel, they can all be notated in Layer 1, and playback will be exactly as you want. What this does not take care of is the percussion midi map or percussion layout for the cymbal rack we've loaded. Read on, I've got that covered.
This is for pitched to non-pitched or the reverse. If you are only switching mallet selections use the text expressions and edit the patch number to correspond to appropriate bank slot (slot/patch 1 is soft, 2 is medium, 3 is hard). for this type of 'instrument change' there is no need to use the 'Change Instrument' found in the Utility menu.
When switching from pitched to non-pitched for a partial measure:
1. in the measure you want the non-pitched note, enter the pitch for the sound you wish to hear during playback. This is best done using a midi keyboard.
2. apply a text expression for the instrument change using the VDL expressions which are loaded into the templates.
3. select the appropriate instrument, in the case of our example this would be Cymbal Rack Combo.
4. click EDIT > Playback and enter the patch number which corresponds to the slot in which the non-pitched instrument is loaded, then Apply.
If you hit playback at this point you should hear the mallet part, then see the patch change, then hear the non-pitched sound.
5. to clean up the notation/layout so that the non-pitched sound is not way outside of the staff or mistaken for a marimba note, use the Staff Tool, select the region containing the non-pitched note and apply the Rhythmic Notation Style. This will change that region of the staff to a single line and the notation would be rhythmic (like reading a lead sheet for drum set or a comping part for guitar or piano)
6. apply another text expression to change the patch back to the marimba
This should fix the problem. As stated, playback will be correct and the notation will be acceptable. Following these steps would actually be the answer if you were using the suspended cymbal sounds found at the very top of the marimba and vibe ranges.
For changes longer than 1 measure use the "Change Instrument" utility along with text expressions for the patch changes. You would also need to do a little set up work for the non-pitched instrument. I will post those steps in a follow-up thread.
iMac i7, OS 10.8, 10.9, W7
VDL2.5.5, Finale 2010-14
Kontakt 4-5, various other soft synths