Why do you want to try and rebuild the XAMPP setup? That would probably be far more difficult than it's worth, because the developers of XAMPP have spent a substantial amount of time changing the configurations of each component so they will work together in a simple install. So just adding new versions to XAMPP won't work as far as I know.
Why not instead just stop/disable the current MySQL or completely delete it if you like, then install the new version of MySQL and simply link it in the phpMyAdmin settings. For the most part, that's the only place MySQL ties into XAMPP is through the phpMyAdmin configuration. The other things you mentioned, openssl and sqlite should be just as easy to replace as long as you update the references to it in the configuration files.
That's going to be much easier than trying to rebuild XAMPP and configuring the new versions to integrate with XAMPP.
By the way, they have the development package for download in the download section, http://www.apachefriends.org/download.php?xampp-linux-devel-1.7.tar.gz
if you insist on doing that.