Hi there,
Theoretically we can use Windows API functions to send messages to a specific application. These messages can be used to do a lot of things including activation/deactivation of forms/controls (mouse click substitution) and/or changing text for the same forms/controls (keyboard input substitution).
However, I will need more details before telling you if I am capable of developing your required application.
Wishing you the best,
Ionut Rosca