Technically the inputs that you get by putting yourself into certain situations will have an effect on your brain, like when you choose to learn something.
We have as much agency in this as any other choice, so you can take the pov that either we CAN modify ourselves, or free will doesn't exist. Both are technically correct, but under different viewpoints only. The point the other anon was making still stands though, as of right now there are no NNs complex enough to learn to solve multiple different sets of problems starting from a smaller number of solvable problem sets. We can though.