SWH
I may be wrong - it happens all to frequently! - but clearnances from ATC do not change your category - ie if you are IFR you are IFR, and operate as such throughout the entire flight unless you initiate the change - "changing to vfr".
So I don't think that you are correct when you say that the procedures change with the clearance.
Don't forget that an ATC clearance for a visual approach is merely that - not a change to VFR procedures. ATC use similar words because they convey a meaning that is understood and it is easier to say than "ABC cleared to descend below the lowest safe and ps while you are at it the responsibility for terrain clearance and maintaining the aeroplane within the CTA steps +500 ft has now been effectively transferred to you - don't screw the pooch - contact tower on 120.5 at 5 miles" or words to that effect!
BUT as I say I could be wrong - it would only continue the fine tradition of being completely and utterly wrong!!