Nova, you should break-in your engine using the same fuel that you're going to be running. The fundamental benefit of break-in is to acclimate the engine to conditions similar to how you intend to run the engine. If you break-in the engine with one fuel, then change it after break-in, you're changing the cylinder temperature and pressure, which is against the concept of proper break-in. There are companies that make break-in fuel, but it's not advisable to use it. It's not going to kill the engine to use different fuel for break-in, but in my experience, it's better to stick with the same fuel.

Tate - I didn't catch the part of the discussion to which you're referring, but the purpose of using foil tape or something else to build heat into the engine is typically for running in cool weather conditions. Every cylinder head has a different cooling capacity which suits a particular temperature range. If the ambient temperature range is well below ideal for your particular engine, then the cylinder head will likely provide too much cooling for the engine. Water-cooled engines have a thermostat, which regulates the amount of cooling based on prevailing conditions. Adding tape or a wrist band to the cooling head of a nitro engine is an attempt to do the same. So, once you block a sufficient amount of airflow from the cooling head to get enough temperature into the engine under running conditions, you leave it there until weather conditions get warm enough that it's not needed.