Insulation resistance and leakage current in capacitor
Yes you can but that would be useless in my opinion.
The 10 GOhms is what the manufacturer guarantees, so it can be 20 GOhms but
also 100 GOhms.

In general you do not need to worry about capacitor leakage current provided you observe the polarity (for electrolytic types).

In general your battery will have significantly larger internal leakage !