Replacing dead high voltage cap with similar of lower capacitance.

I had been hoping for an informed reply. It turns out, as I learned since I posted the question, that the high voltage capacitor is part o fhe voltage doubling circuit between the high voltage transformer and the magnetron. If the capacitance is a bit low, it reduces the final voltage - it does not quite "double" - to the magnetron, which results in a small reduction in the power the magnetron delivers, but with zero risk to the circuitry.