The issue isn't about the word different; just whether or not the shots are simultaneous. According to the rulebook (on page 12 in the lower left corner box), you must nominate which unit or units you are shooting before rolling any dice. So the answer is no, you may not shoot the
FMC and then see if it is grounded or not before shooting again.
Edit: I completely misunderstood the question. Sorry! I thought he meant that he would decide to shoot at a different unit! Not the same one! I'm not sure about using the full
BS in that case! My bad!