the windbg will not modify pdb’s age – it only looks it up to match that of executable – the compiler does when it (re)generates executable and debug files.
now, based on the debuginfo.com article, it is not too difficult to arrive at the proper debug directory (of type codeview), match it against PDB7 signature and make modifications to either age or GUID inside an executable. why is that not an option?
i guess, you want to update pdb instead? i’m afraid, pdb is a proprietary format. there’re multiple read-only APIs (dbghelp.dll and dia sdk), but as far as modifications go, you need to guess the details to be able to modify.