Is it permissible to undergo a cosmetic nose surgery to reduce its size when laughing, given that it causes psychological distress that prevents smiling, and that the aim is not to increase beauty but to be able to smile?

It is not permissible to perform cosmetic surgery on the nose unless the nose is outside of its natural shape, with the aim of removing a defect and not merely for beautification. What the questioner feels by way of harm and refraining from laughter is an exaggeration of something that does not warrant it, and he should be content with what Allah has allotted for him.