Is it possible to renew a ticket on oyster at a tube ticket machine and
pay with notes?


yeah, I think so. You wave your oyster at the machine, and can renew your
ticket. Can use card or cash (not sure if you can use prepay stored on the
oyeter itself)

On another note, I noticed a while ago that the P22 tube font has
square commas, full stops, apostrophes etc instead of the tilted square
'diamond' like ones. Does anyone know why this is?

nope - sorry!