I have voted to re-open this question:
This is a question about how to use a very popular Project Management tool to undertake a very common Project Management task. If this question is off-topic then so are very many other questions along the lines of "How do I do [this thing] using MS-Project" and they should also all be closed.
I don't believe this is off-topic in spirit, even if it is when going "by the book", the OP is not asking for toolset recommendations but are, in effect, asking for how to solve a PM problem they are currently experiencing.
I am not sure how the re-open voting process works, but I suppose I am asking here "Should this question be reopened"?