You can put as many offers in as you like, but It is not recommended to have more then one offer because you could be held liable for fulfilling both contracts. However, depending on the initial terms in your short sale offer, ie. settlement date, if any terms are changed in the final approval letter, you have the right to void and cancel your initial offer. Make sure you read your offer.
You can write a contingency in your new offer which states the contract will not become fully ratified until you withdraw your previous offer on the short sale. The new seller, Im sure, will want a short deadline to have the short sale offer withdrawn.ie 24 hours.
In any case, always act in good faith, don't purposely mislead anyone, and you will be fine.
Best of luck.