How can i change text vibration on my Galaxy S3?
In Android each application can control the notifications itself. So if you turn off vibration for calls, texts will still have the option, and so on.
In the case of Hangouts:

Open the application.

Swipe from the left to open the menu (technically it's a navigation drawer).

Tap &quot;Settings&quot;

Tap &quot;SMS&quot;


You can enable/disable vibration here:

(source: techcovered.org)
If you wish to change the intensity/duration/pattern of the vibration you either need an SMS app that supports this feature or root access to your device coupled with a custom kernel that allows this feature.
Alternatively (though you specified you don't want to) you could try an app like Vibrate tools and see if that fits your need. I have not tested this app.