In my experience, that rule really isn't enforced and I think is aimed at the younger individuals who are 12 or 13 who aren't really to be trusted with rocket motors. Obviously use your judgement and ask for help if you don't know what you are doing, but otherwise no one is going to hunt you down or anything because you assembled a reload. As said above, it for the mentor to decide, there are some individuals that aren't up to the task, so I think if you and your mentor are in agreement, you're in the clear