If it's for work you take the hours needed and get it done. If it's a labor of love (your book!) then you invest the time to make it right.
If the workplace won't allocate the time, then I have to use what I do with software I re-write that is at times, a big ball of mud.
I read http://www.laputan.org/mud/ from top to bottom and it gave great ideas about fixing old bad software or documents. There is no magic to doing this work and no click a button to renumber. It's pick your plan of attack and then do it.
Since we always keep backups we are at no times limited to what we can try.
I have a document that was cobbled together. The sections are therefore not in numerical order, which means that I can't make the page numbers appear in the proper order. Instead, they go like this: 1, 5 13,12, 19, 9, 18. I can't delete the section breaks because there is essential formatting associated with each one. And I can't put the sections in numerical order, because that will make it so the whole document doesn't make any sense.
THANK YOU! for any help you can offer.