Judging from a Process Monitor session, it does not appear that Office programs consult the HKLM version of that value, even when the
Identity key exists there. This Office support document (albeit for Office 2013) makes no mention of anything relevant under HKLM. If you have a Pro or Enterprise version of Windows, however, you can take advantage of the Group Policy infrastructure to set a Registry value for all users.
To do that, you can use my open-source program Policy Plus. Note that Policy Plus is still in development, so there could conceivably be bugs - please test on a non-production machine first, or at least back up the
\Windows\System32\GroupPolicy folder. Anyway, once you get the program downloaded, you'll need a REG file corresponding to the change you want to make to each user. Adding the header to the fragment you supplied should do the job:
Windows Registry Editor Version 5.00
Now run Policy Plus and choose Share | Import REG from the menu. You will be prompted for the policy section - choose User, since we want to apply this setting to the user GPO. In the REG import dialog, browse for the REG file you saved; the prefix should be automatically determined for you as
HKEY_CURRENT_USER\. (This is necessary because the POL format uses hive-relative paths.) Click Import and the dialog should go away without any errors. Click File | Save Policies to commit the change to disk. After dismissing the success message, you can close Policy Plus.
You can verify that the appropriate value is set in your per-user Registry. All other users, even ones created before the change, should receive the value when they next log on.