you can use this condition based on any arbitrary class.
editable: function(ui){
return this.hasClass({
rowIndx: ui.rowIndx,
dataIndx: ui.dataIndx,
cls: 'editable'
});
}
and assign/ remove a class to cell at runtime.
grid.addClass({rowIndx: 2, dataIndx: 'revenue', cls: 'editable'} );