Yes, you may apply for an approval in-principle. In fact, you are encouraged to do so before entering into any contract to purchase a restricted property so as to avoid any forfeiture of monies paid in the event you are not granted approval to acquire the property.  
 

If approval is granted, you have to submit the details of the property you intend to purchase within 1 year from the date of the letter of approval.  Otherwise, the approval will lapse and you will have to make a fresh application. There is no extension of validity for the approval in-principle granted.