Open the Parameter pane's option menu (the lined button at the top corner, or right-click the tab) and turn off Consolidate Properties. You should then have two sliders - click the gear icon on one of them (probably the third party one for safety) and select Parameter Settings, then change its label and click Accept. Turn Consolidate Properties back on to make sure that worked, and finally use File>Save As>Support Assets>Morph Asset to resave the changed morph (only)
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Open the Parameter pane's option menu (the lined button at the top corner, or right-click the tab) and turn off Consolidate Properties. You should then have two sliders - click the gear icon on one of them (probably the third party one for safety) and select Parameter Settings, then change its label and click Accept. Turn Consolidate Properties back on to make sure that worked, and finally use File>Save As>Support Assets>Morph Asset to resave the changed morph (only)