I use Final Draft, and the process there to start revisions is to turn on Revision Mode. Part of that action is to select the revision color/name. Any changes you make will be marked to that revision. If you are going to add text that will break page numbering you can indicate you want to use A/B pages. With that option you could add a new page's worth of content to a scene that starts on page 25 and you'd find you now have a page 25 and a page 25A. This preserves the text that starts of page 26 so its easy to merge changes into the script.
When you're done with your revisions you can print out only the changed pages. These sheets can replace the original pages in the script, so if you were to change 2 pages in a script that was already printed out, only those 2 pages need be replaced. No need to print the whole thing.
No. If they were finished there would be no reason to revise them, right? They are considered "Locked" or "Complete" before you turn on revision mode. The whole point of the mode is to make the process of updating existing printed copies of the script as simple as possible. So if you are wholesale changing massive amounts of pages per revision you've probably jumped the gun and shouldn't even be in revision mode.