Not a whole lot. You can maybe do a free flow exhaust and an air intake but you'd have to fab them yourself most likely. Even then you will not see enough gains to upgrade the impeller to a steeper pitch. In other words you're pretty much stuck where you're at with it.
The official answer is yes, but it gets expensive fast. Much better off to upgrade to a higher performance ski. It will be running within its range as compared to at its max and over its max.
Yes and no. You can do it but it will require engine internals to safely run boost such as lower compression pistons. A cam will also be needed to take advantage of the new power and as the NA cam has a different profile that isn't so boost friendly. In the end by the time you did the build yourself you will be over $$4000 in a machine that's worth less. Much easier and cost effective to sell and buy a higher performance ski.
This has been my concern too. I really want to do some modifications on ours soon but thinking about it, it can be really expensive. I'm considering buying a higher performance ski instead.