The SDK LAUNCHER is being phased out for all existing games.
The SDK itself is now just the same collection of tools chilling in the games 'bin' folder.
If you want to create a mod, you must download the standard issue Source SDK and use that to create a mod. Once your mod is created, restart steam, run the game, then you can run tools specific to your mod from the Standard Source SDK.
I've never heard anything about the app ids