<p>What's the best way to unify several overlapping id systems into a unified one while maintaining the old id system.</p>

<p>I have several different ids on my website... (E.g /publisher/1234 and /designer/1234) I would like to unify the ids into a new system, but want to preserve the functionality of the older system.</p>

You can try using
Microsoft's Sign Tool
You download it as part of the Windows SDK for Windows Server 2008 and .NET 3.5. Once downloaded you can use it from the command line like so:
signtool sign /a MyFile.exe
This signs a single executable, using the "best certificate" available. (If you have no certificate, it will show a SignTool error message.)
Or you can try:
signtool signwizard
This will launch a wizard that will walk you through signing your application. (This option is not available after Windows SDK 7.0.)
If you'd like to get a hold of certificate that you can use to test your process of signing the executable you can use the .NET tool
Makecert
.
Certificate Creation Tool (Makecert.exe)
Once you've created your own certificate and have used it to sign your executable, you'll need to manually add it as a Trusted Root CA for your machine in order for
UAC
to tell the user running it that it's from a trusted source.
Important
.
Installing a certificate as ROOT CA will endanger your users privacy. Look what happened with DELL.
You can find more information for accomplishing this both in code and through Windows in:
Stack Overflow question
Install certificates in to the Windows Local user certificate store in C#
Installing a Self-Signed Certificate as a Trusted Root CA in Windows Vista
Hopefully that provides some more information for anyone attempting to do this!