A treasure trove of OS X defaults write tweaks via

Apple Support - How to get old versions of macOS

RoaringApps Crowd-sourced application compatibility for macOS, iOS and Windows.

Apple Support - 32-bit app compatibility with macOS High Sierra 10.13.4 and later
Go64 Quickly scan your disk for applications, see which ones are 32-bit, and find upgrade information with the click of a button.

OS X: Changing or resetting an account password (Snow Leopard and earlier)