Hi there - to answer your questions very quickly and in the order you asked them, yes, no and no!

You will still get exactly the same in-camera choices of frame rates etc before and after the hack, as the hack only affects the way the images are compressed. The only exception to this is that the MJPEG frame rate can be tweaked actually within pTools. Some people change it to a very low value (2fps) as it allows them to do long timelapses without creating huge files. As far as I know you can't adjust any of the others (anyone know more?)

So after you apply the hack, the in-camera controls will be exactly the same, they will just deliver better-quality images. You shoot 25p by using the HBR setting, then tell your editing software that it's 25p progressive footage and you're good to go. The HBR option was added to the GH2 in version 1.1 of the Panasonic firmware, nearly a year after the original firmware was released, and is actually progressive frames saved as 50i. I can only assume they did this 50i thing as part of a workaround because true 25p wasn't possible for some reason. It's generally accepted that it's not as good-looking as the 24p progressive settings. For more see http://www.personal-view.com/talks/discussion/comment/86412#Comment_86412

HBR can be useful though. I use HBR if I'm doing a multicamera music shoot with long takes, because it works flawlessly in the timeline with my existing 25p HD video camcorders and it saves me having to conform anything to make the frame rates match. My video camcorders are a few years old, so the slightly softer HDV footage and the softer HBR pictures match reasonably well. Plus I can then create a DVD for PAL-land as well as HD footage for online. It's such a pain having these two frame rates.

I normally use 24p if I am using the GH2 on its own for my own purposes or for web video, and I want the best possible pictures and I don't need 25p.

For videos with shorter takes where you must have 25p, I guess you also have the option to capture in 24p and speed up to 25p if you have to. You may decide the increase in picture quality by using the proper 24p settings is worth the hassle.