I partially agree with Alex.
Unless you get on a dyno, you'll never know if they've added power at all and that certainly wasn't why you fitted them, was it? I would declare no power gains.
I would however declare everything, BUT that depends on what they're asking for. If they ask for everything that doesn't come with a standard car (Admiral group do this) then you must tell them about the GT pack extras. If they ask for any non-factory fitted mods, then you don't. Read the text, follow it to the best of your ability, and if in doubt just disclose everything and let them make the call.