Pub User, gatbusdriver, legalapproach are spot on, some of you aren't reading the question correctly. teamilk&sugar, you'll have an interview with no tea, milk or sugar.
There are 2 separate issues here.
1. If RVR goes below minima once inside OM (or equivalent position) you may continue approach.
2. If there is a downgrade in aircraft capability inside OM (or equivalent position) you must perform GA.
KISS