The average student will find it hard enough to maintain an accurate approach speed without further complicating matters with a late change of IAS and trim. No - fly the correct POH approach speed in trim all the way to the flare. There won't then be any substantial out-of-trim forces to cope with when finessing the flare.
I fly an instrument approach clean at the normal cruise speed, but decelerate and configure from DH/MDH (500/600 ft these days as I don't need an IR - an IMC rating is entirely adequate) to achieve the correct POH approach speed from about 3-400 ft.