There is no halfway house. You are IFR or VFR. It should be pre planned.
You put the controller in a compromising position.
You need to understand the controllers position. The person who is the subject of this thread didn't understand either.
I understand that, however on the day the weather (cloudbase) lowered rapidly en route against forecast. I had no problem changing to IFR after she reminded me that I was on a VFR crossing after my (minor) IMC excursion, it was the fact that she wanted me to stay at the same altitude and remain VFR that threw me a bit.
I bet there isn't a pilot on this forum that hasn't gone IMC for however short a period while VFR. Although no, having said that I forget that some of you have flown like saints the whole of your lives...