You can not change the behaviour of the default keyboard.
You would need to create a App with a Customkeyboard and these Keyboard must be set as the default keyboard to use (systemsetting).
But there is no example of doing that in B4A. At least i do not remember seeing one. So this is where the problems began ;-) You need to find out how to create a Keyboard with B4A (or with java (and a java wrapper)).