Neil Young -- I Got Beef with Candidate Donald Trump

6:10 PM PT -- Trump's campaign spokesperson tells us they "paid for and obtained the legal right" to use Young's song -- never the less, they won't be using it again.

We're also told there are no hard feelings ... Donald has been and will remain a fan of Neil's music, regardless of politics.

Donald Trump started his presidential run with a heist ... of Neil Young's classic rock anthem, according to the Rock and Roll Hall of Famer.

It made for a hell of an entrance -- Donald and his wife Melania marching up to the podium while Young's "Rockin' In the Free World" blared at Trump Tower. Totally patriotic ... to everyone but Young.

Neil's rep tells us Trump never got permission to use the song for his candidacy announcement, and furthermore -- Neil, a Libertarian and Canadian citizen, is NOT down with Trump's campaign. We're told he's actually backing Vermont Sen. Bernie Sanders.

Donald ... there's always Ted Nugent.