The challenge is to orbit a body with a weak gravitational pull. Lots of corrections. But it will eventually enter an orbit.
The non-spherical shape, and tumbling of comet 67P will impact Rosetta's orbit and will need to constantly be addressed, or the orbit will change shape. The effect could be to change the shape and of the orbit to one which impacts the comet, or the path could be changes to one which causes Rosetta to leave 67P's gravity.