The 2300kgs in centre tank is to do with keeping the pumps submerged until they are updated with modified system.
However, there is a limititation that you can have a max of 2300kgs, but centre tank fuel should be added to the 'load' total to ensure that max ZFW is not exceeded.
In you case of 600kgs in CTR tank, if the pax/cargo/ctr fuel/DOW is total less than max ZFW there should be no structural problem.