So when can you use missles? When I get attacked I want to send a missle to my attacker's doorstep, but GDI won't let me. When does this limitation come off?

after you have broken gdi (2 ss/ps attacks against same country) or you leave gdi.

Thanks for the info

The person you want to missile must have made two or more landgrabs on you or have attacked you with special attacks (ABs or GSs or BRs) or harmful spy missions.

You can provoke your enemy into opening the situation up. So if your enemy has already made one lg on you hit them back however you can - even bouncing a grab is likely to do it. If sufficiently provoked your enemy will hit again and, voila, you are no longer stuck with the gdi rules.

Don't expect things to end with your missile, though. That hit will also be retaliated. So prepare your country for an extended duel with the enemy country.

Use a bunch of spy ops stealing their stuff. They may hit you again... Then you can unload your missiles. Lol