I have updated my Moto G yesterday to Android KitKat (4.4.4.) Before that I have disabled the stock Messaging app and I used Textra SMS app instead. Everything was working fine until the update. Then I was not able to send SMS from Textra or Hangouts because they were crashing. After resetting the app preferences and re-enabling the stock Messaging app, I am able to send SMS again from both the stock app and Textra. But I want to disable stock messaging app again, because it shows the incoming message preview in notification bar, and I don't want that. I want privacy with my SMS. This feature why I use Textra. How can I disable the stock SMS app?
On Moto G the stock Messaging app is an integral part of the system, and should not be disabled even if you install other SMS apps. If you manage to disable it, other 3rd-party SMS apps (like Textra SMS in your case) will start crashing again.
Instead, you can disable the notifications inside the Messaging app by going to menu -> Settings, and un-checking the "Notifications" option: