Change accessibility setting on Mac using terminal
klanomath's answer looks good, but if you're like me and aren't as familiar with SQL, want more granular control (enabling/disabling individual apps instead of all at once), or want a clearer interface to work with, you should check out tccutil.py.

Using tccutil, the command you'd want to run to enable an app is

sudo tccutil -e app.bundle.identifier


For example, if you wanted to enable BetterTouchTool, the command you would run is

sudo tccutil -e com.hegenberg.BetterTouchTool


I'm assuming that if you wanted to enable BetterSnapTool the last part would just be com.hegenberg.BetterSnapTool but I don't have that installed on my computer so I can't verify.

You can easily find the correct bundle identifier by running sudo tccutil -l after you've installed the app and it's asked for accessibility permissions (just look for the identifier that maps to the app you want to grant permissions to). If that doesn't quite work (like if the bundle identifier isn't what you expect it to be), you can find it by viewing the app bundle's contents, finding the Info.plist file, and finding the value for the CFBundleIdentifier key.