I was thinking about going for a Cold Air Intake. Would it make sense to remove the lid, and keep the bottom of the air box? I would leave the bottom in for the sake of maintaining clean air. If so, how would I attach the cone? Here is a pic of where I assume I can pop one on

 

I guess it would be possible to attach a cone with a hose clamp, but it probably wouldn't work too well. Unless you seal off the air filter from the engine, it's just going to suck in hot air which may actually lead to lower performance. Here's someone else who tried it : Home Made Cold Air Intake - Volvo Forum : Volvo Forums

I think you are better off with a K&N filter or something offered by an aftermarket company.

I you are willing to build a shield, then this thread should have some good info : https://volvoforums.com/forum/intake-headers-exhaust-21/home-made-$52-cold-air-intake-5104/