Yes, as far as I know, there’s a way to flip the overlay.
You can do so while scaling the overlay, like this:
@overlay MOTORBIKE scales to -1.000 1.000
See what I did? I put a negative sign before the first scale value (not sure what it’s called).
If you want a vertical flip you should write @overlay MOTORBIKE scales to 1.000 -1.000 which you probably don’t require but I’ll leave this here anyways. 