Yes, you could change your hubs to the Version 9-10 STI 5x114.3 ones, but be aware it is not a cheap exercise unless you can find second hand parts for a good price.
The 5x114.3 front knuckle assembly has a thicker clevis and the hole spacing for the lower shock mounts is different. You either have to use V9-10 front shocks, or have the knuckle machined thinner, and one of the shock mount holes re-drilled to use your existing shocks. Once that's done, just bolt everything on.
You have a couple of options for the rear.... I am not too familiar with the Foresters, but is yours an STI? and if so, does it have the R180 rear diff etc? If you do have an R180 diff, then you should be able to just get a set of V9-10 rear hubs and swap them over with your existing ones. Or, the other option is to use the 5x100 R180 rear hubs, and re-drill them to 5x114.3, and re-fit the studs. They have enough meat in them to be re-drilled, I did this on my old race car and it was fine, BUT, I am guessing your car will have ABS and re-drilling may interfere with the large bolt-on tone rings that I have seen on some of the later rear hubs (my car was a GC8 RA so no ABS etc).
If your car doesn't have an R180 rear end, then you will need to change the rear end to R180 (axles and diff) to make the 5x114 hubs fit your car - just comes down to how much you want to spend, so if that;s out of your budget, the 5x100 to 5x114 adapters would be the far easier/cheaper option (even with a cert).