I also mix the words up in sentences like you do if I know I have trouble with the first letter. Another thing is if I know a particular letter is easy for me to say I try to start sentences with it. For example if "b" is easy I start with but or btw every chance I get. I realized this method is half psychological because after a while of succeeding at pronouncing sentences that are starting with "but" you become confident every time you start talking with it and confidence is key in overcoming stutter. Btw I don't think things you do are bad, I'd say do it if it helps since it's definitely not possible to become unable to talk normally after using those tips too much.