With certain restrictions you can complete or change the DCB or DCBE during execution of your program. You can also determine data set characteristics from information supplied by the data set labels. You can make changes or additions before you open a data set, after you close it, during the DCB OPEN exit routine, or while the data set is open. See DCB OPEN Exit and Filling in the DCB for information about using the DCB OPEN exit routines. Also see z/OS DFSMS Macro Instructions for Data Sets for information about changing DCB fields. (Naturally, you must supply the information before it is needed.)

You should not attempt to change the data set characteristics of a system-managed data set to characteristics that make it ineligible to be system managed. For example, do not specify a data set organization in the DD statement as PS and, after the data set has been allocated to a system-managed volume, change the DCB to specify DSORG=PSU. That causes abnormal end of your program.