Production Switchers

Is it possible to use a custom control to change the saved Set on a Carbonite? or is there another way to easily change sets without having to use the menu keys on the panel?

You could load a file set from a RossTalk Command.

You could build a DashBoard Custom Panel to do this. 

Or using the RossTalk Custom Type in command ability you could setup a device that sends RossTalk Messages to it's own IP address and then build a Custom That sends that RossTalk Message of the file set you would want to load.

What would that RossTalk Command be?

All of the Supported Commands can be found in the online help

http://help.rossvideo.com/carbonite-device/Topics/Protocol/RossTalk/CNT/RT-CNT-Comm.html#topic.RT-CNT

From that link and the manual:

LOADSET name

Performs a recall of a set by name (name). For example, LOADSET set1 loads set1 onto the switcher from the USB. Unlike saving or loading a set from the control panel, RossTalk does not support saving or loading of panel personality settings with the setup. Settings such as color schemes or user button assignments are not included with the set.