Yep, I’ve always said that Killian changing his clothes would be symbolic of his love for Emma and part of the journey of joining her family.
It came in stages: first, giving up revenge, then giving up his ship, and next will be giving up his pirate clothes.
It’s not to erase his identity as a pirate and all he’s been through, but rather integrate with the life he’s chosen. Fact is, he gave up piracy a long time ago—pretty much right after Milah died. He became a pirate to avenge his brother, and he became a villain to avenge Milah, and now he’s become a hero to honor Emma.