After a data set has been defined, you can change some of its attributes using the access method services command, ALTER. You identify the component by name, and specify the new attributes. ALTER can also be used to change an entry-sequenced data set, with the proper attributes, to a linear data set. The contents of the data set are not modified. See z/OS DFSMS Access Method Services Commands for an example of changing an entry-sequenced data set to a linear data set.

You cannot use ALTER to change a fixed-length RRDS into a variable-length RRDS, or vice versa.