This is a heads up: In LO 5.3, the /org.openoffice.Office/Substitution configuration schema is removed, and the com.sun.star.util.PathSubstitution service no longer supports substitutions defined via the /org.openoffice.Office/Substitution/SharePoints configuration set. See <https://bugs.documentfoundation.org/show_bug.cgi?id=102630> "Useless /org.openoffice.Office/Substitution feature" for a rationale.
Should you be using this functionality, contrary to expectations, in a LO extension or other third-party code, please speak up!