I can see why someone might say "No, you can't reshape your pyramid".
If someone has been playing a jack of all trades and suddenly wants to have fewer skills, or has been playing a specialist who now wants to be a jack of all trades, that's a radical shift for the character. Not just "hit a milestone and changed" but a change big enough to leave me wondering if it's the same character.
That said, when we started we didn't know the rules so used a house rule to cover our ignorance - we agreed to play three sessions and after that anyone who felt he needed to move stuff around could. Powers, skills, the shape of the pyramid, redo aspects - if the player wanted to change what was on his sheet so it would match what he wanted to play then he could.
Richard