1. Yes but not easily - it requires you editing the internal contents of the e-book. Easier to just download the new version.
2. If you are downloading from AO3 then each chapter goes into the table of contents. Just pull up the table of contents and click the link to whichever chapter you want to go to. (I assume the Kobo has a way of viewing the ToC as it's pretty standard for eReaders).
NB. If you remove the old version and add the new version to the Calibre record (using the edit metadata option) rather than deleting and adding the entire record then you might be able to update the version on your reader without it being seen as a 'new' book.
no subject
2. If you are downloading from AO3 then each chapter goes into the table of contents. Just pull up the table of contents and click the link to whichever chapter you want to go to. (I assume the Kobo has a way of viewing the ToC as it's pretty standard for eReaders).
NB. If you remove the old version and add the new version to the Calibre record (using the edit metadata option) rather than deleting and adding the entire record then you might be able to update the version on your reader without it being seen as a 'new' book.