After three days working with this thing I think I have a solution so I will post it for anyone else trying to do the same thing.
First let me explain what I am trying to accomplish and a limitation of the solution that I found. I set up splits and voice changes on a per song basis in my Motif RackXS using Multis. Each song has a Multi. If I transmit on channel one the voices that receive on channel one are playable. If a song calls for different voices in different sections I set those up on a different receive channel and change my transmit channel. That way I can switch between voices/splits even while sustaining a note played on the previously selected channel. The limitation I have found is that the Arturia does not consistently save the midi channel for the 2nd part if you set up splits in your Keylab presets. Fortunately I do all of my splits on the synth itself so it's not a problem for me.
The solution for me is to set up presets 1 - 10 to use different channels and configure the buttons so that pressing a snapshot button immediately switches to the same numbered preset.
To be specific here are the steps I took:
1. Start in Midi Control Center (MCC)
2. Select "Snapshots" button 1
3. In the "Selected Control Parameters" section Change the mode to "Keyboard Preset"
4. Change "CC Number" to "1 - Modulation Wheel" (The CC number is the preset number, you can ignore the description)
5. Change the "Channel" parameter to "Panel" to keep the Keylab from sending Modwheel changes to your synth
6. Repeat steps 2 - 5 for the other 9 snapshot buttons using the correct CC/Preset number for each
7. Press "Send to Keyboard" ...to send to the keyboard
8. On the Keylab (not in MMC) press "Edit" and then "Global"
9. Use the "Parameter" encoder to switch to the parameter "Part1 CH"
10. Use the value encoder to change the value to "01"
11. Press the "Store" Button
12. Use the "Value" encoder to select preset 01 (I am using presets 1 - 10, they will map to the knobs and channels better than using 0 - 9)
13. Press down on the "Value" encoder to store the preset and again to confirm the store
14. Repeat steps 8 - 13 for each "Snapshot" button using the corresponding values (For button 2 I set Part1 CH to 2 and store in preset 2 etc.)
After storing presets 1 - 10 I can pull up a multi on my Rack XS and switch channels while playing by pressing any of the Snapshot buttons.
As you can probably see using this method I am limited to transmitting on only 10 of the 16 midi channels but that will not be a problem for me.
I am now thinking I will probably keep the Keylab even though there are a couple of keys that bottom out against metal under the keybed with a loud plastic on metal click even when I'm not playing forcefully. This thing has some glaring flaws but there are also many things I like about it.