Hi there - This is likely going to depend on the by-laws of your Homeowners Association, as well as any other applicable agreements between you, your property and the HOA.
Here are a few things that jump out at me from reading your inquiry:
1) You mention that the HOA is going to "retroactively change" what has been previously approved, and that might not necessarily be the case. More likely, the HOA is going to interpret that specific requirement differently from that point forward. In other words, the HOA is not going likely to fine you for violations over the past 5 years...but will propose to fine you from this point forward.
2) HOAs can only regulate its members as allowed by contract. Therefore, depending on the facts, circumstances and applicable agreements - there may be an argument that the particular activity you've conducted over the past 5 years is unable to be regulated by the HOA. In other words, you'll present the "you snooze you lose" argument, asserting that since you were able to do it for 5 years, you can do it now, and they waived that particular component of the rules.
This depends very heavily on how long you've done this activity, others in the association have done it and on what basis they are attempting to regulate it.
I would suggest that you seek counsel to review the by-laws, agreements, history of land use and more to give you specific answers.