The Community of Disc Golfers and About All Things Disc Golf
Not a recommendation - Fastest way to changed the flight of a disc without "damage" is putting it hot enough water to cause it to warp, but not to the point it would melt. I did this by accident when I first started by dying disc. Not a recommendation....
Dashboard, same thing as above. The heat from being on the dashboard is going to warp the disc, also direct sunlight is going to fade the plastic color.
Vertical vs Horizontal, Vertical. Horizontal is not harmful with one disc but with multiple disc stacked the lower disc will get warped from the extra weight. When stacking vertically I suggest haveing two points of contact on the disc if possible. Mine rest on dowel rods, but if this is not an option then just rotate disc from time to time to prevent one side from being compressed.
Other ways I've heard to break in a disc...again not a recommendation
wrap disc in paper and duct tape edge, throw at hard surface.
throw disc as high as possible to get hard impact on ground.
tomahawk into ground several times
turn disc upside down, add water, microwave (i would never try this)
sanding of the edge (could make the disc illegal for tournament golf)
How to fix a warped disc (back to flat)
Place it flight plate down on a flat surface outside. Depending on the temp and the plastic this could take for a half hour to several hours.
I've also used hot water to fix bubble plastic when the dome bends. A quick drop in hot water will pop it back into place. This also has worked on a few other plastic but not all, Soft top star for example.