punkaolouver finally nailed it.
This is exactly what we do as regular operators into HKG on 07R. Happens frequently. We always shoot the ILS, aware of the possibility of GS fluctuation. The RNAV is available, but we only bother if it's low cloud or vis. If the GS plays up (about 1 in 10 times), just select VS 7-800 fpm or disconnect and hand fly. Easy peasy.
However, this is common sense, experience and airmanship we're talking about here... Sadly not something prevalent in many operators in this neck of the woods, especially the airline were discussing or the muppets to the north of us.