Replacing a cylinder

Unfortunately yes. You have to follow the Lycoming procedure – there is a Service Letter on it (some previous threads).

You will spend hundreds or more on avgas doing that, until the oil consumption stabilises. My recent data is here.

M89-7R1 is the SB descibing the procedure. Mike Busch doubts that the use of straight oil makes any difference. I used it anyway last time for about ten hours.

AFAIK there is little evidence that – for a frequently flown engine – the oil type makes much difference to anything. Camguard makes a difference to corrosion protection and it reduces the wear rate of the hard metals, but the effect will be negligible over the few weeks or months in question here. You cannot use Camguard during the running-in period.