If you don't open any apps, Mail, iTunes, iPhoto, the libraries may not get upgraded. Once they are they will not be compatible with Lion.
Really you should not install Mavericks without making a backup of your original OS, either use Carbon Copy Cloner to make a clone or Time Machine backup.
Assuming you have now installed Mavericks, give it a fair go. If you want to go back to Lion you will need to do said backups on an external disk first, as you will either need to boot into an external disk and do an erase/install of the computer with the Lion installer and then transfer back you user data.
Alternatively, if you have it available, use Internet Recovery, which will install the computer's original operating system. You'll still need to have saved your user account to an external disk.
http://support.apple.com/kb/HT4718