Sorry it took me so long to notice this question. I'm kinda surprised no one has jumped on it.
There are rules pertaining to forerunners and there is a section, 605, in the ACR and in the FIS ICR entitled Forerunners.
1. Forerunners must be participant members of USSA to forerun a USSA-sanctioned race and the ICR states that "The organizer is obliged to provide at least three qualified forerunners who meet all regulations of the ICR similar to all participating competitors." I read that to mean forerunners for a FIS event must be paying FIS licensing fees.
2. The forerunner must be able to ski the course in racing fashion. Not stated in this portion of the rule, but pretty much understood, it is the forerunners' responsibility to set a good line through the un-raced course, giving early competitors a shot at a course that has already been skied in racing fashion.
3. Forerunners are not permitted to start in the competition (which means a woman competitor cannot forerun for the men and a male competitor cannot forerun for the women) See the definitions of discipline, event and competition in the annual update and review.
4. The times of forerunners are not published.
5. The jury determines the forerunners and their start order.
Regarding your last question, "Or is everything up to the TD?", ski races are run by a jury made up of the TD (appointed by the governing body), the referee and assistant referee if required (appointed by the TD) and the Chief of Race (a member of the Organizing Committee who is always a member of the jury). There is only one special time when the TD (who has the tie-breaking vote on the jury) can override a jury decision. If the vote is on one of safety and the referee and chief of race have both voted to allow an unsafe situation, the TD can over ride them and make the decision in the interest of safety.
