Responses
It just has to be within an accetable range. He's not allowed to do things that's way off common sence, considering the time period he's in. He can't gather materials and make a plane, cure an illness with high tech, or sth similar. But introducing a new marketing tactic should be fine, since sharp ones would be able to create it iwithout prior knowledge in that period as well.
But I thought he wasn't allowed to use any knowledge from the real world??