Guter: What happens to the areas that already got "radio visibility" (on normal diff.)? Will they get "darkened" again?
edit: Still having the timer bug. It's frozen on 00:04. Will that be fixed with a patch?
That all depends on whether you are changing from medium to easy or hard mode. Hard mode gives you only 1 radio radius range in a mission (with the exception of missions that have multiple radios), so going from med to hard will remove all the repeaters you placed in the level so far.
Going from med to easy will do the opposite, instead of removing the repeater you have already placed, it will add repeaters to all other powersources in the current mission.
As for the timer bug, I am not sure what the status of that is, because it would be fixed by my colleague and not me (i do the art). I do know that we have mostly shifted focus off of Signal Ops, seeing as we no longer have any money to keep up maintenance on the project. We are hoping that future influx of income from sales will allow us to spend a little more time fixing the more minor bugs, but as of yet that has not happened. Needless to say, we have logged the issue you are having, and if is possible for us to fix it in the future, we will.
If you are enjoying Signal Ops thus far, we urge you to spread the word and help us get greenlit on Steam. Getting onto Steam will help us get the resources we need to further support the game, as well as develop new features (such as Linux/MAC ports, and maybe even a VS mode)!