Both of your issues are already being addressed in a future release. We're working on implementing support for Site Keys for Install from Web and in that same update we're improving that parameter as well as the version banner notice. See below what to expect once Site Keys have been implemented.

New Banner:


New Description:


Banner tells you what to disable and gives you a link directly to the parameter. Parameter then explains it impacts CB build releases.

If you do not want to be notified about build releases then again turn off Plugin Version Checking within CB > Configuration > Integrations. That is the sole check for build releases. If that's off the version check file used by build version checking will never be requested by your site. You will still be notified of stable releases by Joomla. You can also just flat out unpublish the banner if you don't want it as it's simply an Administrator module in Extensions > Modules.

The big notification for nightly/weekly build shows up again although I have turned on Version Checking to Manual.

Setting version checking to manual does not disable that banner. This is being addressed in the same release that's improving the banner as shown in my previous reply.

It is quite annoying to be welcomed by this announcements everyday I log in.

I'm shocked you're annoyed by receiving updates that fix bugs and add features.

Why did this change 4 or 6 weeks ago?

People kept sitting on installs that were months out of date and constantly posting about bugs we've already fixed. It became a significant problem with people failing to keep their installs up to date. We could release more stable releases, but you'll be right back to square 1 with being annoyed by a banner to update except it'll be a stable version instead of build version which makes no difference as they're all tested the same. I don't see how else to please you other than simply turn off version checking entirely and you'll be responsible for manually checking for new releases.