tune help when changing to a smaller lsa pulley

Curious:

Pontiac G8 was professionally tuned for added LSA supercharger (running stock pulleys) last summer. Ran great no complaints.
Now thinking of maybe installing 2.55 upper (likely nothing else except maybe larger intercooler rad-not the brick)),
At the time of my first tune- tuner quoted me about 100-150 to re modify tune if i changed pulley in future. I realize its not much $$ but what exactly is modified in tune when increasing boost from pulley ratio change?
it now runs a blended tune.
its only really under power enrichment right? as not much to do with volumetric efficiency tables as bypass plate in blower is open when not under power enrichment.
Any info is welcome

Realistically you should look at everything as you are going to move more air. Also watch your injector duty cycle to make sure you don't run out of injector. Better safe than sorry.

What he said... You'll at the very least need 850 injectors. Stock injectors are only good for around 600 to the tires and the pulley will put you above that. You'll also want a CAI if you don't already have one to support it. Snout has to come off to do the pulley, so make sure to upgrade the isolator while your at it.

As far as the tune goes - depends on how aggressive the original was as to whether or not timing will need adjusting. Both air models will need adjusting. Injectors if done. Torque model will need tweaking if tuned correctly.

you will also need to look into fuel pump upgrade and boost a pump

you may face pressure drops with more boost and larger injectors

You will run out of injectors and the pump will depend on the age of the vehicle, the LSA pump is borderline at best and relies on the FSCM fuel pressure sensor to compensate in the injector duty for falling pressure. As the injector delta gets higher due to raised boost pressure and falling fuel pressure you eventually run out of injector duty, you can fit a larger injector but if the pump is not 100% you will end up with fuel pressure dropping below 300kpa. Expect to need injectors and a new stock pump with a limited life expectancy or preferably upgrade the fuel system. The gains are diminished with more boost due to the limited timing that can be run as far as peak power although they are a lot more punchy. I'd suggest a cam.