Yes, you can watch the original effects or the new effects. The editing is always the same because they specifically wanted to avoid the "Special Edition problem". Aside from enhanced mattes and new space scenes, there are a handful of phaser effect changes and a couple Gorn blinks. No other effort was made to fix mistakes or visible zippers or obvious stunt men...Gaffer Tape said:
The Blu-ray uses alternate angles to branch both versions. As far as I know (but I've never actually seen it, as I have no Blu-ray player), that means ALL the changes will reverted if you choose to watch it that way.
My frustration is that they didn't have the time or budget to do it all the way. Sometimes phaser effects or other effects are enhanced and its awesome. Other episodes they didn't have time so they just left everything the same. I wish they had done an all or nothing approach. Another frustration is that they couldn't go all the way back to the original elements, so the fades to the new space effects have to start before the original fade did.