Not sure if you can modify the gesture; you could always create a custom UILongPressGestureRecognizer but not sure how you'd get the pressed row.
In another way, you can implement it in:
- (void)shinobiDataGrid:(ShinobiDataGrid *)grid willEndReorderingRow:(SDataGridRow *)row
NSLog(@"Long press on row: %ld", (long)row.rowIndex);
// Pop up a menu.
I couldn't find a "shouldReorderRow" delegate method so as an ugly work around in case the user does move the row, you could reload the grid here to restore the rows:
- (void)shinobiDataGrid:(ShinobiDataGrid *)grid didReorderRow:(SDataGridRow *)rowSwitched withRow:(SDataGridRow *)rowSwitchedWith
// Reload the grid to restore the row order.