Considering that the thread you are linking to is from 2001 and is probably created during early vBulletin 2.0 stages. A lot (read: everything) has changed since and solutions provided will for sure not work on later releases.
You do not need a modification for this with 3.x, it is standard functionality.
AdminCP -> User Profile Fields -> User Profile Field Manager -> {{ Location }} -> Edit -> Field Searchable on Members List: Yes
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