I want to reinstall my system so I would have fresh Mac OS X. Is there a way how can I export/backup all content of my Keychain Access (all certificates and other things) and then after reinstall to import it back? Thanks
Save the keychain folder(/Users/[UserName]/Library/Keychains) on an external drive or in the cloud.
After the reinstall, then replace the "/Users/[UserName]/Library/Keychains" with the data you saved in the step before.
(Some of your keys may already be saved in iCloud)