The inner tube sizing will have more room to play with than the tire sizing. The 700c tubes are interchangeable with 27 inch, but the tires are not.
I tried exactly what you are asking about several years ago on my early-80s Schwinn Le Tour. Eventually I bent a rim beyond repair and ended up converting it to 700c wheels anyway. That would be pretty involved just to open up more tire options, but you could go that route.
Sheldon Brown shows that a 700c tire won't fit on a 27 inch wheel.
The inner tube sizing will have more room to play with than the tire sizing. The 700c tubes are interchangeable with 27 inch, but the tires are not.
I tried exactly what you are asking about several years ago on my early-80s Schwinn Le Tour. Eventually I bent a rim beyond repair and ended up converting it to 700c wheels anyway. That would be pretty involved just to open up more tire options, but you could go that route.