My dad was anything but sentimental about his remains. Said I could just chuck him in the dumpster after he died for all he cared.
However, I chose to have his remains made into stones/pebbles, which were then given to people who attended his remembrance. I tasked them with leaving a stone in a natural setting, which served multiple purposes: 1) it would return my dad (who was a naturalist) back to nature, 2) it would give people a way to participate in the remembrance, and 3) when people would visit the place where the stone was left, they would think of my dad long after his stone had eroded.
Ultimately, whatever is done to someone's remains is for the benefit of friends and family. It's not about what the deceased would want, since they're not alive to enjoy it anyway. Rather, it's about what his friends and family want.
So anyway, if you want to dress your deceased friend in a jacket because it makes you happy, go ahead and do it man. Your deceased friend would want you to be happy.