It makes no sense to have to use a weapon before reforging it. The main reason was probably to stop people from gaining Level 10 weapons quickly. With the new heat crystal system, that is no longer a problem.
Instead, make heat be a property tied to the knight instead (think "heat of battle").
- Each knight has a heat bar which naturally depletes over time, but can be recharged using heat gathered while exploring the clockworks (same mechanic as now).