Increasing 'lb' does not change the engine, for most cases it was just adding stronger parts.
It says so on the source I posted.
I don't fully understand what you mean though.
Sorry for not having been clear. What is the threshold of an engine being "different" we hardly need to discuss as this is often of an arbitrary nature.
The point of the discussion was, that if you have an (old) aspirated engine, designed to run on low octane fuel, and you supply it with high-octane fuel, it would not give you extra power when operated in the same regime.
The examples you provided, where changes on the supercharger were made possible due to the octane rating, is a different thing. Merlins etc. are high performance supercharged engines that are mainly limited in their power output through pre-detonating fuel air mixture when compression gets excessive. In those engines, fuel quality is one parameter that allows you to generate more power by either just let the engine run at higher rpm (if the engine block tolerates that) and in consequence have increased boost by the same blower, or adjust fan and/or gearing of the blower to get higher compression (more air) at the same rpm. Most Merlin variants exist because of the latter modifications.
In all cases with the engines you mentioned, you run the engine in a different regime than with the lesser grade fuel in order to get more power. If you call that a new engine or not, this decision I leave to you.