Citado no Manual de Procedimentos do Instrumento, página 4-6:
APPROACH CLEARANCE
The approach clearance provides guidance to a position from where you can execute the approach, and it also clears you to fly that approach. If only one approach pro- cedure exists, or if ATC authorizes you to execute the approach procedure of your choice, the clearance may be worded as simply as “… cleared for approach.” If ATC wants to restrict you to a specific approach, the controller names the approach in the clearance—for example, “…cleared ILS Runway 35 Right approach.”
When the landing will be made on a runway that is not aligned with the approach being flown, the controller may issue a circling approach clearance, such as “…cleared for VOR Runway 17 approach, circle to land Runway 23.”
Então, se eles nomearem a abordagem, você estará restrito a essa abordagem.
Eu procurei no restante do livro por itens especificamente relacionados a operações não-gigantes e não encontrei nada que contradizesse isso.