I have no qualms with "improvising" tools and innovative repair techniques, BUT the only chain that ever broke on me (tens of thousands of miles at 220-275lbs)
was a chain I "reused" a pin on, and used a proper chain tool to reinstall it. You don't want a chain to break, especially sprinting at your max effort, it would really hurt.
And the "final fit" of the pin is really critical, I don't think a hammer would get both ends pressed in correctly.

PS. I spent a few hours once trying to fix one without a chain tool, never again, the aggravation and frustration trying to fiddle
with such small crap with big fingers is 100% not worth it IMHO.

I would suggest

1) Get a chain tool and a replacement pin (if you don't know which it is maybe your LBS can help)
2) Get a master link and use that, probably the best bet/cheapest fix now.
3) Get a chain tool and a new chain and replace the old one.