Basically, don't ask, don't tell.
Meter going in reverse only applies to the older "spinning disc" meters, sadly the electronic ones do not go backwards ????
Doing this is, of course, definitely not permitted. So don't let the meter man see it going backwards and definitely don't end up with a negative meter reading when the man comes.
Getting caught generally means a slap on the wrist and the installation of a meter that won't go in reverse.
If you have an electronic meter and don't want to join the official feed-in system then a hybrid inverter and battery storage will be the way forwards I'm afraid ????