Hi. Fellow Lefty designer here. Here is my trick: if there is a difference in orientation due to color changes, I honestly mirror the picture before I send out the tester call or on advertisements. That way, the majority will have the end product end up the way they expect. Alternatively, I have had very good reception to posting a split pic like you did labeled which hand it uses.
Actually changing the pattern is trickier than you think as the actual stitches slant the opposite direction so the stitches will come together differently.
Also, if you are crocheting in continuous rounds if you just read the round backwards, then there will be a definite jig in the beginning/ end of the rounds as you will essentially be trying to attach the beginning of a round with the end of the next round.
The only way to almost take care of this is if you instead write patterns using slst and ch1 to join rounds and not a spiral. Then reading each round backwards would almost work except for the different slant of the stitches.
Moral of the story: just show them the mirrored pic to begin with. :)