This needs a registry update, customize the string value with your OST path.
This is for Office 2013, but can be used with Office 2007/2003 by changing the “15.0” version option.
Windows Registry Editor Version 5.00 [HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\outlook] "ForceOSTPath"=string:D:\My Documents\Outlook |
Once the registry update has been completed, create a new profile (which defaults to this location) and move the old .ost to this directory (same file-name and overwrite the existing .ost)