The places to change for a CPU serial number change are,
 
1)  SYSTEM NETID on the 190 disk.  Don't forget to change the 190
    disk for all your CMS's, CMS4, OLDCMS, CMS, NEWCMS, CMS55, ...
 
2)  The first few lines in the directory.  With DIRMAINT 1.4, you
    need to change the XXXXX YYYYY file on DIRMAINT's xxx disk.
 
3)  VMTAPE:  Change the VMTAPE CONFIG file on VMTAPE's 191 disk,
             a.k.a. VMTSHR 500.
 
4)  HCPSYS.
 
5)  That stupid CPUID MODULE.  The source is on