Sounds like you need some guidance.
Your question leaves me and I'm sure others a little bit confused. You're at the right place to get help. Just be a little more specific.
What kind of engine are you speaking of?
There are no multi-cylinder bike engines out there.
A single cylinder engine only has 1 piston.
TiM...
Yes, of course you can, but you will need a metric crescent wrench and make sure there are no parakeets within 50 yards. Actually better make it 100 yards or meters to be safe if this is your first time.
Yes you can run on one piston ring for a while.
Put the one ring in the top of course.
Some of the racers do this but change the piston and ring often.