How change the SDF defined model runtime? (to lock a revolute joint)

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Hi, I want to add a Lock property to a revolute joint, I mean I want to Lock the joint so that there is no DOF for that joint anymore and then release the lock again. How can I handle it? I think maybe I should 1 - add a fixed joint exactly in the revolute joint position so it will prevent the revolute joint revolution. 2 - or change the <xyz> to 0 0 0 To do that I should change the model (SDF) runtime. how can I do that in gazebo? Thanks,