Updating Keychain entry manually prevents next access from GUI tools afterwards: Always asks for permission
For macOS Sierra:

To add an object and allow access (with user prompt), use the "-T Application" option. (Several applications can be used)

security add-generic-password -a "account" -s "name" -w 'password' -c aapl -T /Applications/Utilities/Keychain\ Access.app/Contents/MacOS/Keychain\ Access


Then to allow access without user prompt you need to modify the ACL for the object:

security -v set-generic-password-partition-list -s "name" -S "apple:"


The partition-list syntax is not very well documented. You might be able to see how Tunnelblick uses the ACL from the output of "security dump-keychain".

Source: man security