3.a. second sentence, line 2: “No part of the jaw/hammer may extend more than 1.0 cm beyond the base.” Is it correct to assume that this is confined to the set and unset conditions only?

Yes, that is correct. The jaw/hammer in its manufactured range of motion may rotate to extend more 1.0 cm beyond the base provided that all other requirements are met and that the mousetrap used is considered safe.