Advanced Preferences: add Apply

[jidanni]

Add an "Apply" choice at the bottom of Advanced Preferences, as "OK" closes the window
making a big hassle to get back in if the user is not finished yet.

[stoecker]

Simply don't click OK if you are not finished.

[jidanni]

I'm thinking of the case where one wants to test how a certain value
looks when set to 7, 8, 9, 10 etc. without having to dig it back out
of the menus each try.

[michael2402]

We have a lot of preferences that don't need a restart to be applied now, so it makes sense for me.

[stoecker]

The expert preferences are not meant to be used. Actually I don't want it to be too easy to use them. If an option becomes important enough that users regularly change it, then we will add an interface for it. Otherwise everybody who uses expert prefs will have to live with the restrictions.