A character may start the game with Skills that have the condition that only certain sub-areas of that skill may be chosen when the HP is created. The HP can learn other sub-areas of the skill only if the opportunity presents itself, it does not interfere with any Vows, and the gamemaster approves the learning.
Example: Chin Su' Nygen is a Monk HP. His restricted skill is Criminal Activities, Physical. If Chin Su' Nygen's STEEP was 42, he would normally receive four sub-areas of knowledge. Since this is a skill with restricted sub-areas he can only learn the three which are allowed. If Chin Su' Nygen was to begin to develop the darker side of his HP while adventuring the gamemaster may allow him to develop the other aspect of this skill (This may not sit well with Chin's former instructors).