So.
In order to redownload Warcraft 3 Reign of Chaos and The Frozen Throne, you are supposed to go to your account game list https://account.battle.net/games and click on the download link for an installer.
This installer forces Reforged to download.
This no longer happens.
Instead, the link takes you to a support article which offers alternate download links https://eu.battle.net/support/en/article/256212
These alternate download links tell you that you are installing Reign of Choas or The Frozen Throne.
They do not.
What you currently get, is the default Bnet installer whcih does not force the startup for Reforged to run the old version only version of the client.
Edit:
Thanks to the Wayback Machine, the old install link has been found.
If you are affected by the mismanagement that has lead to this situation, you can go to the official blizard link https://downloader.battle.net/download/getInstaller?os=win&installer=Warcraft-III-Setup.exe which will attempt to download the Installer that will force Reforged to install with the modern content locked.
You will still require a Bnet account with the original codes redeemed to play
