Upsized motor to 24mm.
The modification is fairly simple. I sanded down the plastic tail cone until the opening was the same as the inner diameter of a BT-50 motor mount tube. I used a BT-50 to BT-55 centering ring for the forward end of the motor mount and epoxied the aft end of the motor mount into the tail cone, being careful to center the tail cone properly. The key to flight worthiness is adding extra weight to the nose cone. I used 30 minute epoxy which I poured into the nose cone through the small opening at the base. I then dropped small 1/8 oz. lead fishing sinkers through the hole into the epoxy pool.
I've flown the rocket twice using Estes D12-5s. Both times I had excellent, straight-up flights and pretty impressive altitudes. I almost lost the rocket the first time when I launched just before dawn. The white rocket is difficult to see in the early morning light. I thought that perhaps the motor's ejection charge blew the motor out the back and I had lost it when finally we saw the chute about 200' above us.
A good upgrade to get a small rocket flying very high. I recommend perhaps a different paint scheme, it's a small rocket and the additional altitude makes it easier to lose.