An IMCR changes the VFR rules
No it most certainly does not. It changes the licence privileges.
Please also note that UK VFR limits are different from ICAO and thus from most other countries (some of which have further differences). The most important one being that in controlled airspace C, D and E it is normally a requirement to meet the 1500m horizontally and 1000ft vertically from cloud requirements regardless of level.
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IO540,
Perhaps ICAO wrongly give pilots some credit for judgement. Remember that when required it is a minimum and there is nothing stopping a pilot from being more than the minimum.
As you may be aware, it is unusual to meet the requirements for an appropriate level for cruising flight i.e. odd+500 or even+500 as appropriate under ICAO and manage to get only 1000ft separation from cloud. I find that it is usually obvious that there will be less than 1000ft or there is well more.
regards,
DFC