can somebody tell me, what will happen, if I activate the keyword feature later on.
Will the existing sgaddresses with no korrekt keyword be blocked after starting keyword feture?
OR
Is the keyword feature only for the generation of new sgaddresses?
I assume you mean watchword and watchword protection doesn't monitor your database itself, but only the creation of new database entries.
It doesn't know what you have in your current database, only that it won't let new addresses be created unless they have XY in them.
So yes, your current "watchword free" addresses will keep working.