It is possible to change a prisoner's security category. This can be done by clicking on a prisoner and changing the appropriate setting in the menu that comes up.
The arrival of new prisoners can only be stopped if Continuous Intake is disabled. If it is, to stop the arrival of new prisoners, you must close your prison to all three prisoner categories. To turn on/off the prisoner intake, go to the reports menu, select the prisoners tab, and close all three levels.
Low Risk Edit
Low Risk Prisoners generally have only very short sentences and will not be with you very long. Many of them leave your prison in a matter of days. Low Risk prisoners tend to leave before finishing any programs and are therefore generally not worth educating. Low Risk prisoners tend to tunnel less often and are more easily kept content than Normal or High Risk prisoners. They will still attempt to flee when a clear path is available, no matter how long their remaining sentence is, and they are also highly active in contraband activities. Low Risk prisoners will make use of contraband thrown over the walls.
Normal Risk Edit
Normal Risk prisoners have low to medium sentences and will therefore be with you for a reasonable amount of time. Normal Risk prisoners tend to tunnel less often than High Risk prisoners, but will become disgruntled faster than Low Risk prisoners. Normal Risk prisoners are more likely to be involved in a riot, are highly active with contraband, and will flee whenever the opportunity rises. Normal Risk prisoners will make use of contraband thrown over the walls.
High Risk Edit
High Risk prisoners tend to have unreasonably long sentences that last far beyond the lifespan of a normal human being. They will however not die in your prison unless they are murdered, so they will be with you almost forever. High Risk prisoners become disgruntled extremely fast, start riots very fast, and are extremely prone to tunneling. They will obtain any and all contraband they can, and flee as soon as they can. High Risk prisoners will make use of contraband thrown over the walls.