Re: can you stretch a wetsuit hat ?
I think you'll find the difficult aspect of trying to stretch the hat circumference is that's where the stitching is. Most likely stretching the seams will damage or rip them. I had a similar hood and gained a little bit more comfort by removing the bill (“peak”). That allowed a little more stretch and also removed the stitches that were irritating my forehead.
You might consult the manufacturer or the shop you purchased the hood from. They may have an idea. Sometimes I take things like this to the wetsuit repair lady. She sometimes has good ideas for solving these funny little problems that seem to bother no one except me.