Here is a way to mirror hair, the instructions that follow are for conforming hair, but the process is similar for prop hair.

1). Load the hair, don't conform it. Zero the translations and rotations of the hair figure. In P9/PP2012, you can do that via the Zero Figure button in the Figure menu.

2). With the hair's Neck actor selected, create a magnet. Select the Mag Base, make sure its xTran is zero.

3). Select the Mag Zone, make sure its xTran is zero, set its scale to be 5000.0.

4). Select the Mag, set its xScale to be 0.001.

5). Select the hair's Neck actor, from the Object menu, select 'Spawn Morph Target', Name the morph "Mirror", click 'OK'. Delete the magnet. Set the Mirror morph to a value of 2.0.

6). Open the Grouping Tool. Select 'Reverse normals'. Close the Grouping Tool.

7). Memorize the hair, then Save the hair figure to a the figures library (you will not be able to save it to the hair library).

As far as the morphs go, some may still work correctly, particularly those that only affect up-down motion of the hair, or front back motion. Morphs that only affect side-side motion should work but will require a negative dial value. Morphs that affect side-side and also affect up-down or front-back, will not work correctly.