The teeth look fine in the top photo, does it actually need changing?
I was also wondering if I could get away with it! I will be fitting a new cassette, middle ring (a thin profile one with tabs should just slip over the spider) and chain. So am slightly worried it will be horrid and slip on the small ring. but maybe you are right 🙂
A big dumb question: “big bolt in the middle”… What crank bolt? On square, ISIS and X-Type I’ve done, there is an 8mm hex crank bolt you unscrew to reveal the the inside-thread of the crank (where you screw in the crank puller) and the face of the axle with its own inside thread (which held the crank bolt).
But there are no bolts to remove here. Unless you are referring to the 10mm hex-shaped hole inside, but that just looks like the end of the axle to me. Bit confused, sorry