Q and Answer: Can Wide Lapels Be Slimmed?
DT asks: Is it possible to have wide lapels slimmed?
The answer to this question, generally speaking, is yes. That doesn’t make it advisable, though.
The main reason is that it is a very time-consuming operation for your tailor, and for that reason will be quite expensive. You can also run into trouble around the button hole - if it’s a real hole, it can’t be moved. In most cases, this dramatically limits the amount of slimming one might be able to do.
So: possible, but not recommendable.