Add downgrade option to Updater

Due to some bugs in the latest version (6.1.1.310), I intended to downgrade to version 6.1.1.309. However, I've encountered an issue as there doesn't seem to be an option to specifically downgrade to this version. Only the last version of latest stable and beta are supported for installation, which poses a challenge for my specific use case since the last stable version is too outdated.

Furthermore, I've observed that the downloaded package "platform*.wyu" is deleted after installation. For individuals with slow internet connections, it would be beneficial to have the option to download a local installer or to save the "platform*.wyu" file locally for future reinstalls.