If you have a date or other way to split the database into two parts: the UTF-8 data and the iso-latin-1 data: then you could split the tables, and convert one of them automatically and rejoin both. BUT you need to find the criterion to do that split. Might be easy if you know when it changed and you have e.g. automatic timestamps for a last update, or excellent logs - but it might be nearly impossible just as well.
To get the entire database into a text editor all you need is mysqldump (commandline).
You can edit that text (it's actually a collection of sql commands ready to feed to mysql to restore the database).