You might be a king or a little street zsweeper, but sooner or later you will dance with the reaper

src/transaction_builder.cpp

@@ -104,6 +104,11 @@ bool TransactionBuilder::AddOpRetLast()
     return true;
 }
 
+void TransactionBuilder::SetExpiryHeight(int nHeight)
+{
+    this->mtx.nExpiryHeight = nHeight;
+}
+
 void TransactionBuilder::AddOpRet(CScript &s)
 {
     opReturn.emplace(CScript(s));