If you upgrade to 14.0 from 12.6 without an IPL (and have not performed an IPL with 14.0 installed), you can go back to 12.6 without an IPL. If you have performed an IPL after making 14.0 active, perform an IPL to go back to 12.6.  

To use the features of the Release 12.6, you can back out from 14.0 to 12.6.

Follow these steps:

1. Stop tape processing and backup the VMF and Alog data sets using your currently installed versions of CATVMFB and CATALOGB procedures.

2. Stop CTS if active.

3. Remove the currently installed version of the 14.0 OSI intercepts.

   PRODUCT(CA TLMS) VERSION(TLE0) INIT(TLE0INIT) -
   PARM(REINIT,OSI=NO) -
   LOADLIB(hlq.TLMS.r14.CTAPLINK)

4. Empty the 14.0 members from the 12.6 link-listed library. If you used a Dynamic LNKLST to add the 14.0 library ahead of the existing 12.6 library, simply remove the 14.0 library from the LNKLST and issue a "F LLA,REFRESH" command.
5. Copy the entire contents of the backed up 12.6 load library back into the 12.6 link-listed library and issue a "F LLA,REFRESH" command.

6. Load 12.6 dynamically by executing the CAS9 procedure with the following control statements for CA TLMS Tape Library Management System in CARIMPRM:

   PRODUCT(CA TLMS) VERSION(TLC6) INIT(TLC6INIT) -
   PARM(REINIT,LPA=ALL) -
   LOADLIB(hlq.TLMS.r126.CTAPLINK)
    
   PRODUCT(CA TLMS) VERSION(TLC6) INIT(TLC6INIT) -
   PARM(REINIT,OSI=YES) -
   LOADLIB(hlq.TLMS.r126.CTAPLINK)

7. Start CTS using the hlq.TLMS.r126 libraries.
8. If you are using the CA TLMS TLTP interface, log out from TSO completely and then log back on again.