Intended behaviour:
$ sysctl user.localbase
user.localbase: /usr/local
$ pkgconf --dump-personality
Triplet: default
DefaultSearchPaths: /usr/local/libdata/pkgconfig:/usr/libdata/pkgconfig:/usr/local/share/pkgconfig
SystemIncludePaths: /usr/include
SystemLibraryPaths: /usr/lib
$ LOCALBASE=/opt/vendor pkgconf --dump-personality
Triplet: default
DefaultSearchPaths: /opt/vendor/libdata/pkgconfig:/usr/libdata/pkgconfig:/opt/vendor/share/pkgconfig
SystemIncludePaths: /usr/include
SystemLibraryPaths: /usr/lib
$ sudo sysctl -w user.localbase=/opt/vendor2
user.localbase: /usr/local -> /opt/vendor2
$ pkgconf --dump-personality
Triplet: default
DefaultSearchPaths: /opt/vendor2/libdata/pkgconfig:/usr/libdata/pkgconfig:/opt/vendor2/share/pkgconfig
SystemIncludePaths: /usr/include
SystemLibraryPaths: /usr/lib