Would re-introducing a half-penny coin increase the money supply? No. Basically, as long as you maintain proportionality, you can re-denominate currency (or shares for that matter) at will.

More relevantly, nothing stops you from creating a tradeable note that says "redeemable for 1 bitcoin from <trusted authority>" and then using those as currency.

This happened with gold, and also would happen if we saw a true bitcoin bank rather than bitcoin wallet -- they'd pay a bit of interest, and in return would pool their deposits and use some fraction of them to generate revenue through other channels.

bitcoin-B would not be bitcoins, nobody would use them, and they would at best be tulip bulbs.

Unless you are using them to do something different then currency.

No. Gold production has definitely become more energy intensive, and in this regard it is somewhat similar to bitcoin. HOWEVER, with bitcoin, marginal mining cost is a function of cumulative supply. As supply reaches 21M, marginal cost goes to infinity, and it doesn't matter what technology you bring to bear. Whereas with gold, technological advances have moved the equivalent of bitcoin's 21M to 42M, 84M, etc. The maximum possible supply increases. Yes, of course at some point the technological maximum will reach the physical maximum, but we aren't there yet.

The result of all this is that gold supply has grown with the economy over the past 500 years. It may be deflationary relative to fiat currency, but it is nothing like the deflationary profile of bitcoin, not at all.