Don't know for hairs but for voice the toolset seems required, editing the xml I quoted seems change nothing.You can also use the Dragon Age Toolset for that. Open a savegame (*.das), navigate to SAVEGAMES_PLAYERCHAR and near the bottom should be an entry "SAVEGAME_PLAYER_SOUNDSET". Change the string to one of the names found in Dragon Age\packages\core\audio\vo\en-us\vo\ss_pc_*
For instance, the entry for my rogue was "ss_pc_felf_wise" for a female, wise elf.
Not sure about the hair, I assume it's in SAVEGAME_APPEARANCE, maybe ORIGINAL_TYPE? But I guess it would change more than just the hairdo.