Smart Keyboard apk mod

Is it possible (and legal) for me to tear down the apk of Smart Keyboard?
If so, are there any lines that I can edit to modify the position and text size of Alternative Labels (I want them to be positioned above main letter but on the right not on the center)? Also, can the number row have another key design different from the main keys?
I’m asking these because I want to create, for my own use, a skin that looks like LG V30 or G6 stock keyboard.