Downgrade Xamarin.iOS in Visual Studio 2017

Question

I have to use an older version of Xamarin.iOS (10.12) because our Mac building server runs on an older version, the problem is that I am not allowed to update the Xamarin.iOS framework on the Mac.

I wasn't able to find older installers for Visual Studio 2017 nor Xamarin. There was also a blog post about the Xamarin Updater but the extension is no longer available.

Is it possible to downgrade Visual Studio 2017 and/or its components and if yes how?

Solution

Visual Studio for Windows
Downgrading Xamarin.iOS to the version 10.12 in Visual Studio means that you need to downgrade VS to the version 15.3.
You need to contact the support team for the download link since they provide only the link for the version N-1.

I'll just leave the links, they may be useful to someone.
For Xamarin Studio:
It's possible, either downloading Xamarin.iOS from here:

https://dl.xamarin.com/MonoTouch/Mac/xamarin.ios-10.12.0.18.pkg

or directly from the repository, which contains every version:

https://github.com/xamarin/xamarin-macios/releases