Originally Posted by cybmole
thus most authors/publishers would do their styling in epub or in html & then-to-epub; & convert to mobi only to sell on amazon ?
Yes, most MOBI ebooks a created from either ePub or HTML source files.
It is not possible to edit the MOBI format itself as it is a compiled file. To make changes you have to extract the contents by decompiling it or convert it to some other format. You can then edit the pieces and use the edited pieces to create a new MOBI.