if I add gap to the core ,can I run it at higher flux, the max. flux for this core about 200mT, if I add gap can I run it at 400mT?

 

Not exactly.

Adding a gap will not change the saturation flux density. Since adding a gap is equivalent to increasing the magnetic path length, the gap will allow you to have more amper-turns for a given flux density and thus permitting the core to store more energy.