A system for an adjustably flexible downhole tool includes first and second connector ends each configured to connect to adjacent downhole tools and a shaft extending between the first and second connector ends. The shaft is configured to bend in response to passing through curved portions of a wellbore. The adjustably flexible downhole tool also includes an outer sleeve disposed around at least a portion of the shaft and extending from the first connector end in a direction toward the second connector end and at least one adjustable member configured to move axially, with respect to the shaft, from a first position to a second position to increase bending stiffness and/or torsional stiffness of the adjustably flexible downhole tool. The at least one adjustable member at least partially restrains bending of the shaft in the second position.