In any bureaucratic organization, the basic goals of policy are set by people at the highest levels, but the policies must be carried out by the people at the lower levels. This gives the people at the lower levels opportunities to subvert or “displace” the goals that have been set by the people in charge. A prison system is definitely a bureaucratic organization. That means that there are opportunities for bureaucrats in the system to displace the goal of rehabilitation.
One way for bureaucrats to do this would be to take their time coming up with programs that could be used to rehabilitate prisoners. The bureaucrats would have to be the ones to design the programs and they could drag their feet. They could conduct long studies to attempt to figure out what types of programs were best. This would take so long that the goals might be changed by future political leaders.
It would also be possible for officials in each prison to simply fail to implement any programs. They would not refuse to implement them, but they could just not give the orders needed to set up the program. This would delay implementation of the goals until higher-ups got around to investigating what was going on in each prison and directly ordering that something be done.
These are some possible ways for bureaucrats to displace the goals that are set by the people at the top of the organization.