C. Players may not make post-production modification of discs which alter their original flight characteristics. This rule does not forbid inevitable wear and tear from usage during play or the moderate sanding of discs to smooth molding imperfections or scrape marks. Discs excessively sanded or painted with a material of detectable thickness are illegal. See sections 802.01 D, E and F
I'd just like to point out that the "wear and tear" merely needs to be "inevitable," not "unintentional." The exception does explicitly apply only to the "wear and tear" from "usage during play." But in a casual round, you can tee off from wherever you want, and throw in any direction you want, and take as many practice throws as you want. And who says you have to be a course? I practice in my yard or a fielde all the time. If I throw a disc during tournament that has wear and tear from such practice, have I broken the rule? Of course not.
So as long as the wear and tear is the result of throwing the disc (as opposed to using a blade or other tool), or does not go beyond "light sanding," such that it is indistinguishable from "normal wear and tear," then I don't see any problem in the player buying a disc between turnament rounds and trowing it straight up in the air in the parking lot several times without catching it, or even running over it with their car (as can occur unintentionally during tournament play if the disc goes OB on the freeway). I mean, seriously, who cares.
But if you whip out a heat gun and a pair of tongs, or a hot plate, boiling pot, and 20 pound free weight, and go to work in front of the TD, or tell him that you modded the disc in that fashion, then you deserve to get penalized. I have a hard time seeing a TD enforce this rule in circumstances other than that, as long as the results modifications don't deviate from the type of wear and tear that we view as normal.