To do the mod, you'll need a cutting implement (a dremel is probably the best).
First thing is to remove the snow grate which is at the bottom of the airbox - undo the screws holding the lid down, remove the filter and then at the bottom of the box, there is the snow grate. It should just lift out. But if you're heavy hand and impatient such as myself, the fins on the grate will snap.
The next part is the noisy part - you'll need to remove the front air duct of the intake, and cut away on the right side of the duct to open it up. (I have some pictures I'll upload). Using the dremel is easiest as you can cut away and sand it down smooth after. (The red circled area on the picture is what you need to cut. When the intake is out, you'll see what the left side looks like, and you're essentially making the right side look the same).
Once done, you'll need one of these to block off the engine bay side of the intake:
https://progressiveparts.com/genuin...ate-for-mqb-platform-2-0tsi-engines-5q0129849 (Second Picture shows it is installed)
Re-install the intake back onto the car and you've essentially turned your airbox into a very cheap 'Pikey' R600.
Most people tend to upgrade the panel filter at the same time, and then the intake hose, turbo elbow and muffler delete. Progressive Parts actually sell the complete kit for £340 (including the blanking plate above):
https://progressiveparts.com/vaagsport-high-flow-intake-package-1-8t-2-0t-mqb-ea888-gen-3-engines
So for £340, you get a bit more intake noise, better airflow and better performance as a result.
Stock airbox's with the upgraded filter, hose and elbow have been said to be great up to stage 2. A stock 2016 Cupra
290 ran the pikey R600 mod on the Progressive Parts rolling road day and put out 311 bhp.
If you're local to Preston area, I actually have my stock airbox with the cutout and blanking plate already if you fancied a swap?