A few things in here that sounded just a bit fuzzy to me...
1. Under AMA Rules, the flier signals the start of an Official flight by turning to inverted at the end of the first wingover in the Reverse Wingover figure. You might confuse and tick off the judges if you do the first wingover, then pull out upright, but they should recognize that you were not declaring the start of Official scoring at that point. (You could, if the wingover sounded okay, start the "Officializing" wingover with the inverted recovery a lap or two after bailing out...)
2. UNLESS you have declared your flight Official (by the inverted turn out of the first wingover), your flight can - should - be considered an Attempt. Even where a meet adds the two Official flight scores to determine placing, an Attempt is not an Official. Most meets allow three Attempts to get two Official scores, whether they use best single flight, or best totalled score. Some might even allow two Attempts per round to score one Official flight...
3. I don't think FAI current rules have the AMA declaration thing. You signal to start engine and your flight is Official. (Haven't read the new Encyclopedia F-A-I-tica in the past few days, so I may have some part of this not quite precisely accurate.)
But, to the first actual question, when I crash at a contest, I bite back the tears, pick up the pieces, and tell those who commiserate at my loss that, "I'd never liked that model anyway. Now I can build something RIGHT..."
Incidentally, I think it is looser than we've been saying, here, to substitute a 'backup' for the initially entered model. The judges should accept the flier's statement that he considers the first model unflyable for whatever reason. (If the backup model hasn't been Appearance Judged, it should be before it flies, and THAT appearance score entered on the scoresheet.)