Don't do this. It's likely possible in some cases, but consider
* It's downright wrong
* You're committing fraud, you're extracting something of value based on false statements (and in some cases false promises of future business)
* If you don't do a good job of your 'photoshopping' the airline or hotel will realize you're trying to pull a fast one, could suspend your account and you'd lose all your miles/points
* These things are usually once in a lifetime anyway, why not save them till you really need it (when you're traveling enough to earn it)?