It depends on the person as to how easy it is to switch back and forth between tue two weights.Finacially it is obviously easier to replace them one at a time. That being said i would replace them starting weakest to strongest as it is easier to ball down and you would be less likely to need to go back and forth in weights.
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Arsenal: Mega Friction, S-75, Break Point x 2, Break x2,Clutch x,Maniac,Awakening,Lunatic,SX-1,Link,Hype urethane,Global Globe, 14# golden globe

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For some people, it could be a timing issue which would impact your release and your score.  Go practice using a 15lb or 16lb ball first for one game, then try changing to the other weight for the next game and see how long it takes you to make a good shot.  Like I said, everyone is different and you may have no problems.