frogprince said,
"Thesaurus.com give a string of synonyms for conspire, several of which at least muddy Tunesmith's argument"

I don't think so.

For example, " To Plan" can be a synonym for "To Conspire " as in, for example, The terrorists planned/conspired to blow up the building.

But, in the song the couple are planning their future, by the fire, and conspire doesn't fit.

Would you be happy, for example if the couple in the song talked about "conspiring to get married?",