To change blade off-set and/or shorten the paddle, cut it in the middle, this is the lowest stress part of the shaft. DONT think of cutting it near the blade!
To rejoin you use an internal ferrule or composite or aluminum, alternatively use a an external sleeve that slides over the join (each should be at least 6" IMO). If you want use both methods together. Use epoxy to set them in place. If either is not the perfect diameter, use a bit of painters tape to build up small contact areas and use the expoxy liberally.
I have done this in the middle of a shaft and its bomber...no issues.