It worked really well.

It took me a little bit to figure it out, so for those who may need to know how to do it in the future:
1) Download the FaceReplacer2) Make sure you have Python 2.7 (download/install if needed)3) Extract FaceReplacer into MyDocuments/Bioware/Dragon Age/Characters4) Run it
-Select 'character'; then select the save game file with the PC face that you want and set it as source
-Select 'face' and click 'new face file' and save it as a .mor (this doesn't actually extract the .mor yet, you have to then click 'set destination' and 'save destination file' for the new .mor to be saved)
5) Now you've extracted the .mor file with your character's face on it!
6) If you want to use the face to replace an NPC, just rename it to that NPC's .mor filename (e.g. for Alistair it's hm_genfl_alistair.mor) and place it in the override folder in MyDocuments/Bioware/Dragon Age/packages/core/override