Hi, I want to share my experience with compiling Principia from sources. I wanted to add KSP 1.7.1 support because waiting one whole month is unbearable and I was encouraged by the fact that there are virtually no changes in KSP support since 1.4.0.
There's good tutorial how to build Principia from sources on project wiki (https://github.com/mockingbirdnest/Principia/blob/master/documentation/Setup.md) but I wanted to use VS 2019 and as little dependencies as possible. It turned out quite well because in the end I only needed:
VS 2019 with C++ and C# support
Windows SDK 10.0.18362
.NET Framework 4.7.2 SDK (and Targeting Pack)
I also noticed that recommended PS command "$GitPromptSettings..." is unnecessary (it's just an optimization).
It was necessary to patch all project files (including Google dependencies) to target .NET framework v4.7.2 (was v4.5, v4.5.2 and v4.6), SDK 10.0.18362.0 instead of others, and even change platform toolset to v142 (currently v141) - i.e. it was possible to completely switch to the most beautiful VS 2019. Great thing is that it compiles and passes tests!
As for the changes for 1.7.1, there aren't that many (depends how thorough you want to be). For gaming it's enough to replace all 1.7.0 to 1.7.1, 1_7_0 to 1_7_1 and fix ksp_plugin_adapter.cs on line 207 to (Versioning.version_minor == 7 && Versioning.Revision <= 1))).
It compiles for some time and if it fails, you have to start from the beginning. When I managed to build Google dependencies, I commented them out (build_solutions($dependencies)) in rebuild_all_solutions.ps1 to speed things up a bit. I had to compile Principia about four times before I catched all the errors but it's definitely doable and there's no dark magic. :-)