Yes exactly , in some FEA software you can create a conector/zero length element to create an constraint between a Master node and slave node , when the coordinates of the two node are the same you can associate the stiffness of the spring or any assigned material with a degree of freedom. In that way you can create hinges , releases , flexible supports or assign rotational stiffness to the 4,5 and 6 DOF.
I want to Constraint a node with a flexible supports modeled by Force/deformation relationship "K (kN/m) "
Sure, I’ve used that in the past in other FEA packages. I haven’t tried it on ccx but I’m not sure if there are any restrictions. Look at pages 138-139 of the manual, there are different spring elements. Maybe one of those is suitable for your goal.