It could be done through a naming convention in the industry. To call one BTC, 1/100 of the current BTC. It can also be done through a fork but I doubt they would do that just for the psychological effect
I think it's one of the reasons people keep saying bitcoin btc is too expensive, they don't realize you can buy/own fractional bitcoins. My phone has 0.2 btc at the most, and usually less than 0.1 btc 1 satoshi is 100 milionth of a bitcoin 0.00000001 7 leading zeroes. During the bull market of 2013/14, a new unit was proposed as the default on wallets, but it reverted back. It's called millibit 0.01 which is equivalent to $227 at this moment. Electrum wallet on the phone does $ conversion (and other fiat currencies) so you can put any fractional bitcoin amount in there for example 0.035974 btc but it's dependent on the exchange configured on the electrum wallet which is selectable.
yes, you can send 1/100th of a bitcoin. I suppose you could write a smart contract for 1/100th or issue a token, or fork again, or...
They can and they should have done it 3 years ago when they went over 10K for the first time. But of course if you split, the message of "only 21 million ever" becomes "only 2.1 billion ever", that just doesn't sound that good. But because the system and implementing new features are extremely inflexible, getting consensus on anything is almost impossible so maybe at 100K they will do it.