In order for a K&N air filter to work on your Jonsered 801, you'd have to mount a "stack" adaptor directly to the carburetor and then mount a standard K&N air filter to that. If you did that, you would not be able to put your air filter cover back on.
Also- when fitting a different type of air filter to a saw, you have to re-adjust your carburetor and possibly put a new carb kit in it. The aftermarket air filter will have more flow and you will cause a lean running condition if you do not richen the adjustments.