A horological assembly for a horological regulating member, including a balance spring (25) having a coiled flexible strip (2); a device for adjusting its rigidity which includes a flexible element (5) arranged in series with the strip and connecting one end (4) of said strip to a rigid support (17), the flexible element having a rigidity greater than that of the strip. The adjustment device includes a pre-stressing device (6) for applying a variable force or torque to the flexible element to vary the rigidity of the flexible element. A stud-holder (1) is configured to suspend the balance spring and includes a main body (30) connected to the flexible element, and a secondary body (33) connected to the pre-stressing device, the secondary body (33) being movable relative to the main body (30) and being connected to the main body by a flexure bearing (20).