It's possible. A few years ago, I started the whole "jelquing" thing - in particular this thing for the head that I read on a pumper forum online called "Head Blasters".
I've since stopped...but the gains from that first round are actually still with me. My head used to be sort of arrow headed but after a month of this process, it became much more rounded with a pronounced helmut on the dorsal/top. Also - it's much harder and firmer when I get an erection and the skin is now smooth and really shiny/maxed out looking.
The hole used to be a slit but when hard, but it's a nicer more open looking hole. The only problem is my piss stream is not as clean and straight as it used to be. My last squirt is like a spray.
I should really continue but I just don't have the privacy anymore. However, I sincerely believe getting a bigger penis head is possible. My half-hearted efforts have had permanent gains going on almost 3 years this November.
I used to warm up with a warm rag and I used Burt's Bees Oil to jelque with. I miss that time because I had so much for private time to do this. Not anymore. A few guys have called my dick a "nice knob" so I guess I did something right although I DO NOT have the much beloved mushroom head. It's just more even with the shaft now.
My dick also has two very big veins on the dorsal that I never had before either so there's something to that whole process.