some manufacturers tell you not to have spacers above the stem (other than a very small one to get the top cap to hit right.) the reason is that it moves the clamping force of the stem below the portion of the steerer tube which is reinforced by the compression plug.

This appears to make some sense if you use a glued in aluminum sleeve to hold the start nut.

That said I wouldn't worry about it, particularly on the temporary basis, as long as you're careful torqueing the stem bolts.