This is a User-assignable preference that remains when RMX is opened the next time.
Multi Patches are capable of saving MIDI Learn Assignments. Most of the time, you will likely wish to keep the current active MIDI Learn Assignments when loading a Multi Patch. In certain circumstances—e.g. special live performance requirements—you may want the MIDI Learn assignments to be loaded with the Multi patch and replace the current MIDI Learn assignments.
When this menu item is checked, RMX leaves the current active MIDI Learn Assignments in place and does not use the ones saved in the Multi. This is the default behavior.
When this menu item is unchecked, RMX overwrites all the current MIDI Learn Assignments with the MIDI Learn settings saved in the Multi. If the Multi had no saved MIDI Learn Assignments, then all the current MIDI Learns are erased. In other words, ALL of the sounds and settings of the plug-in can be loaded by switching to a new Multi Patch.