Ever heard of infinite ride? Same concept you're thinking of just done with a very fancy machine. All boards gain flex over time and riding them. Take a new board that doesn't have pretensioned fiber glass in it and flex it the first day in the shop you'll hear all the fiberglass cracking along with the epoxy. That right there is the start of it breaking in.
heres a link to people putting rocker in their skis. SKIING RULZ
snowboards are all glass and wood, so heat is a must to keep any bend in the board. When epoxy is heated above the temperature it was cured at (150-180F in normal production) the epoxy will soften up. At this time it can be reshaped and then allowed to cure again. I am going to try with an older board first here when i find some time. I plan to uses boiling water as it is 212f and i would not have to worry about overheating the surface with a hair dryer or a heat gun. Just need to make my bending jig small enough to fit in the tub.