Originally Posted by Hitch
In short, No.
Every time you make edits to the source for a mobi, you have to rebuild it. One edit; one hundred edits, doesn't matter. You rebuild it. That's why most of us make the ePUBs first, make all the various edits, etc., therein, and then build the finalized ePUB into a mobi file. If you're determined to do mobi only, then what AnemicOak said is the only way: unpack an existing mobi with mobiunpack, edit the bits you want with an html editor, and then rebuild the mobi using KindleGen or KindlePreviewer.
Exactly true. The mobi format should be treated like a binary file because that is what it is. KF8 is a compiled ePub. KF7 is proprietary compiled file. You wouldn't directly edit a binary executable and you shouldn't try and edit a compiled mobi.