In KeePassX you can add extra attributes for an Entry.
This attributes can only be Clear-text type.

Add support for Extra Password Attributes (like PIN, Secret Answer, etc) obviously encrypted

Original KeePassX issue: https://dev.keepassx.org/issues/540
KeePass feature: http://keepass.info/help/v2/entry.html (Advanced -> Custom Strings)