You most likely wont be changing the injector just the nozzles that are the very tip. It is common that engines come from the factory "detuned" and adding things like larger nozzles can actually give you better mileage but I wouldn't mess with it. More fuel without more air is going to increase your EGTs (exhaust gas temps) which is bad for a diesel
You don't have a turbo on that one but it is a direct injection engine which is much more efficient than the IDIs so to answer your question yes you can change the nozzle size but it's not as simple as that. If you do mess with it install an EGT gauge before the mods and keep track of what's going on after the mods. If you can't do the labor yourself you'll be throwing money
out the window.
For ex: I have installed larger nozzles on a TDI that I am working on but I also have installed a higher flow turbo, a custom injection pump
(with a manually adjustable max fuel screw) and an EGT guage to keep track of what the mods are doing to the EGTs.