The file you edited was almost certainly
Contents/Info.plist. You usually just need to change
CFBundleVersion to a number greater than the one listed in the
MinimumVersionRequirements section of Apple's blacklist:
Other options include changing the
CFBundleIdentifier in the application's
info.plist, or simply editing
Exceptions.plist so the application/version is no longer blacklisted (if System Integrity Protection is disabled).
Before you bother with that, however, there's an easier way to temporarily launch and app and see whether or not it will work. Instead of double clicking the
.app file, try running the executable in
Contents/macOS directly. This should bypass Apple's blacklist.
I have some bad news—none of this is likely to work. Preview is a lot more complex than Calculator.
If you want to go further, start by using
otool -l to see what frameworks a binary depends on:
otool -l /System/Library/CoreServices/CoolApp.app/Contents/MacOS/CoolApp
install_name_tool to change which copy of a framework is used by a binary:
install_name_tool -change /Library/Frameworks/Foo.framework/Versions/A/Foo @executable_path/../Frameworks/Foo-From-Lion.framework/Versions/A/Foo Bar.app/Contents/MacOS/Bar
But it still probably won't be enough for Preview, either.
Here is all of the code I had to inject to make the 10.8 version of QuickTime work in 10.9 (thereby adding back support for third-party codecs such as Perian, which I subsequently updated to support VP9, the format used for 4K Youtube videos). https://github.com/Wowfunhappy/QuickTime-Fixer/blob/master/QuickTimeFixer/main.m. It took weeks to figure out what code was needed; I finished it only because the pandemic left me stuck inside over Christmas and New Years. And I was only bringing QuickTime one version ahead, not seven versions!