How easy is it to replace an air flow meter on a Subaru impreza wrx wagon?

Depends which one you have to start with? Some are a drop in element with two screws and others are the whole maf housing which bolts onto the airbox.

Neither are that hard but just need to be careful you don't drop or damage it

It's a 2002 Impreza WRX, thinking of buying it, so was getting an idea before jumoing in.

I'd check which one it is as they range from a ton to nearly 400.

If your looking to modify you may be able to have it mapped out. Not to sure on new age cars if it's possible