It's pasteurised to stop you from making mead, not because it does anything to Clostridium spores.
If you want to start your own culture from scratch there are established practices for culturing "wild" yeast from the environment.
Not seeing this and instead going for 'hehe my little dude, pasteurisation doesn't destroy the sugar, you can still add yeast and ferment it' doesn't come across as particularly impressive from my perspective.
I never said that? It's well known that heat alters honey.
Obviously the purpose of pasteurization is either preservation or food safety (but I repeat myself) as opposed to preventing people from making mead. I claim no particular knowledge of which specific microorganisms are primarily responsible for the spoilage that might otherwise occur, nor the precise consequences of such spoilage.