Let's say you are not LVP qualified , no LTS qualified , just flying a cessna 172 , IFR equipped , coming to land to an airport with 550/125/75 , are you allowed to shoot the approach by regulation?
Yes you may shoot the approach, because in a 172 you will be less than 60 kts before the mid-point of a multi-RVR runway, so the mid- and stop-end RVRs are not "relevant" to you.
If your landing performance indicates you will cross the mid-point at > 60 kts, then the mid-point RVR is relevant, and must at least be 125m if reported (since this is lower than the CAT I touchdown RVR requirement of 550m).
Remember, relevant means over 60 kts at that portion of the runway.
(The rules differ by country... e.g., in the FAA world only the touchdown RVR is controlling for CAT I. The mid- and stop-end RVRs are always advisory for CAT I).