I guess you missed the right way to achieve that. If I had to do it, I'd first upgrade XF 1.4 to 1.5 then upgrade XenTag to it's 1.5 version, there is an awesome tag import feature which import all your XenTag data to XF built-in tags system. Then you could safely uninstall or disable XenTag and upgrade XF 1.5 to 2.0.
Uses The DragonByte User Tagging mod adds multiple new features to your site, including extending the user mention feature to also work for user groups (auto-complete enabled). It also adds the ability to add Twitter-style hash tags to your...
Hash tags: Typing # then any given word will generate a hash tag that links to a search result containing all posts where this hash tag is used. Auto-complete is supported for existing hash tags. Works in posts and user profiles. Users can also watch hash tags from the results page.