If you don't do anything with a Joker, you may like the beam. It will probably have a larger hot spot and a smoother transition to the spill beam. Throw will suffer depending on how far the focus is off.
If ya want throw, it's like Harry said, just shave (sand) some off 'till you like it. .003 to .005 per try is about right. .015 is about what you need (in theory) to compenate for the Joker die height difference.
There is a lot of manufacturing variance in the actual focal point in some reflectors. It's a case by case thing. Ya can't just remove .015 and expect great results every time.
If you use a Joker reflector, ya get the beam that the designer intended (less the manufacturing variables) without the fun of sanding.