Step 1: You will need...
A chainsaw chain
An air cutting or grinding tool. (A bench grinder will probably not work)
A Punch tool.
A hammer (Ball-peen works best)
Decorative paint (optional)
Step 3: Cutting and rebuilding
Find where you marked earlier and shave off the surface of the pin with your air tool.
You will probably need a punch to get it out.
Do the same thing on the other end of the chain and put the two loose ends together.
Insert the pin and hammer the top end (with your ball-peen hammer) so that it flattens out over the opening as shown.