As Realtors, we cannot offer legal advice. You really need to consult with an attorney.
Also, I'm not sure what you mean by "home ownership has changed." Do you mean the HOA board has changed, and now they're trying to change the HOA guidelines and restrictions on the placement of satellite dishes? Do you have anything in writing indicating that they did indeed give you approval 4 years ago? These questions are coming from my own curiosity, but best advice is still to consult with a local lawyer.
However if you had HOA approval installed 4 years ago... odd they now want it relocated. If approved was there any concession stating "in future may require relocated"...