And not dropping them would be, as well!
Technically, you still haven't committed theft, since the intent must be present at the time of the taking.
OTOH, in practical terms (aside from the fact that its still a crime either way), the fact that you did keep it is something that a prosecutor will often have very little trouble convincing a jury is clear evidence that you intended to keep it when you took it.
> It's a copy, and you did not intend to buy it anyway so it's all right
Criminal conversion (in the general case) or joyriding (sometimes a separate offense in the automotive case) is not "all right"; just because it is a different criminal offense than (general or auto) theft, its still a crime, which is kind of the opposite of "all right" from the perspective of the legal system.
WTF?
"It's not theft, therefore it's alright" ... where did you pick up that logic?
It's really not that difficult, you can simply look up what these terms mean instead of inventing your own definitions. "Depriving someone of money" is not the definition of theft. And it not only isn't, it would be a braindead definition if it were. Suddenly, buying from your competitor would be theft. Accidentally dropping your dishes would be theft. Pretty much everything would be theft under that definition.