have some problem, i am new to SSDs and i installed win 7 system on it, and then i was looking around in the samsung magician soft and saw an option for over provisioning... i googled a bit what that is and it looks like it is a good thing to have turned on, but ... is it possible to enable it and assign a 10% of space to it while i am on system which is installed on this drive? i did not find the answer for this anywhere...
You do not want to over provision unless you are using the drive in an enterprise application. It will eat up valuable space and while it can extend drive life, that is only in very heavy use situations -- Samsung has already kept some space available. You can just keep an eye on your space utilization and try not to go over 80% or so for maximum performance.
Also, optimize your drive, read THIS very good guide.
edit: and just to answer your original question, yes you can use Magician to over provision after the OS install if you haven't done anything crazy like made multiple partitions on your SSD.