A lot of words function like this. E.g., "believer".
When a christian asks me if I'm a believer I might say yes.
But then I'd probably say no if a wiccan asked me the same question.
Obviously, that doesn't mean that everyone (or no one) is a believer once you fix some additional context.
So in summary, according to the sense in which the USFG is using the term, you're simply not a terrorist.
Everything else about your post is just a slippery slope argument, which may or may not be valid, but certainly isn't well-substantiated.
Terms of art will always borrow and re-define colloquial language. Do programmers aspire to 1984 because they re-appropriate the word functional?
Defining an explicit list of "terrorist organization"s may or may not seek to redefine the term terrorist, but it is not tantamount to willful restatement of established historical fact (a la "always been at war").
No one would seriously would assert that the term-of-art definition of terrorist == the dictionary denotation of terrorist. That is the meaningful line in the sand between mere rhetorical ploy and outright democratic totalitarianism.
For better or worse the definition is being expanded such that we're all going to be classified as terrorists soon enough. Terrorists have fewer rights than the average citizen, so its inevitable.
Am I a terrorist? Well, yes, yes I am. My wife donated some money to our local mainline Catholic church and they've participated in some anti-abortion activities and some define that as financial support of terrorism. I was in the US military and I never did anything personally, but the army certainly has participated in acts that are terrorist from the point of view of other countries. Some of the worst terrorist acts happened before I was even alive, but I bet PLA members and Hezbollah members don't get a free pass for the same reason. Why the org I voluntarily joined, genocided the Native Americans just a century or so ago, and per the SS standard that makes me not just a terrorist but an unrepentant war criminal. I voted for Trump and campaigning for him is considered a hate crime on college campuses. I'm into electronics and computers and theoretically I could make a radio jammer or write a computer virus, although I'm not into that personally it doesn't sound too hard and a I certainly have the skills and gear necessary.
So in summary we've donated money from the shared checking account to financially support terrorist acts, I willfully joined an active terrorist organization in my youth (although I do have an honorable discharge, so there's that in my favor), I willfully and knowingly have terrorist / hate crime sympathies, and I have proven terrorism related interests and skills and abilities. So yeah, I am a terrorist. Many of you are too. I have to lie on my immigration forms and claim I'm not a terrorist, very annoying having to do that.