D - avoid duplicate altnames.

d - avoid Duplicate altnames.: This instructs OPEN to generate a unique altname for a permfile if a conflict occurs with a name currently in the AFT. See "expl b lib acc.fil" for more details. This option is applicable in TSS only.
The "d" option should be used with care. If the file is already in the AFT, the open operation will fail with a "file busy" status. Without "d", OPEN checks the AFT for permanent files that have the same altname, and removes those files before trying the open operation.