Yamaha VL1 Owner's Manual page 37

Feature Reference Edit Mode
• When the cursor is positioned at the "E1 Name" or "E2 Name" parameter
in the initial EDIT mode display, "Swap" appears above the ¶ button.
Pressing this button exchanges the E1 and E2 data, including the element
names. This function can be used to swap the elements used for the high and
low notes when Key Mode is set to "Unison" and Voice Mode is set to
"Dual". Since E2 always contains data, the Swap function can be use to
temporarily switch elements even when Key Mode is set to "Single".
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