Bluetooth keyboard quick layout change

I have a Logitech bluetooth keyboard for my Samsung 10.5. I want to be able to press a combination of keys that changes the keyboards output/layer from the corrosponding key to predefined sentences or symbols (utf-8). I want to change these predefined stuff easily. Example: I'm writing a text, but need to insert a few sentences or symbols. I press let's say Ctrl + Alt + Shift (or any other) and suddenly the keyboard doesn't write "G" on the screen when I push the G key, but a predefined sentence or a symbol. Then i press Ctrl + Alt + Shift again, and the keyboard works as normal. It's very important that the app doesn't drain the battery and that it doesn't slow down the tablet in general.