Is it possible to change/repair an aircraft tire while in flight?
Accessing hydraulic lines &amp; resevoirs is perfectly straightforward in plenty of aircraft -- the C-130 as one example.  With crew chiefs &amp; their tools &amp; spare parts on board, a temp repair on a hydraulic line would be possible. Highly unusual, but possible. Spare fluid is common enough to have on-board to replenish the resevoirs.

However, access to the tires... Nope.  I can't think of anything where you could do that, and it would have to be a designed-in capability. Typically, crew-accessible areas are pressurized, but where the wheels retract, aren't.  You have things like access to unpressurized bomb bays, and in unpressurized aircraft that's not a barrier, but still... If there are designs where the crew can access the tires in flight, I'm not picturing them.

As noted elsewhere, landing with a flat tire isn't typically a big deal.