Hi Woof,
I guess the situation would largely differ from country to country. Best is to assertain yourself with the relevant laws applicable.
The AIP would normally indicate what type of traffic is permitted in a circuit, and in my experience this is normally VFR only for unmanned airfields. (Could of-course be diff in other parts of the world). If this is the case (VFR only), its pretty self explanatory that IFR would have to be cancelled before entering the circuit.
Another issue would of-course be what NAV-aids are available at such fields. How would an IFR navigate into a field where no nav-aid available?
Regards.