When running for long distances (42k, 65k) I have noticed that at kilometer 30, my feets comming to get a lot of pain, I think that is something normal, but I think it could be the cushion of my shoes that is not helping anymore, because of the long distance.. so this is something usual? should I change my shoes in the middle of the race so my feets don't get tired at that distance?
Yes! It's quite common for runners to change shoes, socks, shirts, etc. in the middle of a race. If you feel that it would be helpful for you then try it out in training and then implement it in some race.
Update: answering @Pacerier's question
Ultras have regular aid stations where you can get water (at least) and food. Many ultras will note particular aid stations as having drop bags. You give a bag to the volunteers at the start and it will arrive at that aid station (hopefully). Alternatively, you might have crew who will drive from aid station to aid station and help you out.
It's important to read the racer manual for a particular race and consider your plan.