How did you purchase your tickets? If you already have hard copies, then there may not be much you can do. If it's simply an add-on to a package, then you should have no problem calling to make the adjustment. Worst case scenario: Cancel the whole thing and rebook with different tickets.
I don't think the parade and fireworks will sell out in advance (except maybe on the busiest days) especially now that they've started allowing people to get more FPs one at a time after they've used their original three. It just doesn't make sense to pre-book something with such a high capacity, even if it's not from the best location. To me the only reason those are included in FP+ at all is as carrots for the people who suck at planning for Disney. If all the Tier 1 attractions sold out before the park opened, then all the people who buy their tickets at the gate would be frustrated. That's not to say other people won't book them, but they won't be a high priority for anyone who books their FPs in advance at all. Therefore, if you link your tickets to
MDE immediately after it's possible, you will likely easily get at least those towards the end of your trip, if that's what you want.
Bottom line: I haven't read a single advice column on FP+ that has screamed - book parades and fireworks!
Soarin, Test Track, and the Mine Train are slightly different stories, but even those I doubt will sell out completely in advance. You may not get the exact time you want, but I expect you'll be able to get something.
If those are the only 3 things that you're concerned about, then by using Rope Drop and possibly Extra Magic Hours, you'll likely be able to get in to see them without too much drama, if you plan well.
Maybe plan your first 2 days at Animal Kingdom and Hollywood Studios, so you have a few day buffer to get what you want at the other two parks.
Sooo....my planning spreadsheet had some errors and I'm balking a bit at the price of our trip. A large part of the problem is the airfare which I haven't booked yet, so I'm overestimating, but it's still more than we've ever spent on a trip before. Probably because this one is a bit longer, and we won't be using the Armed Forces Salute tickets for the first time since 2009.