The shifting affirmations are to collect & shift your focus from all other things to the procedure of piano shifting method. Whenever you feel distracted (even the tiniest), affirm yourself & get back to the method.  So, you can affirm whenever & as many times you want to. Also, it’s up to you how you want to affirm. You can mumble/whisper the affirmations. Or, you can revise it in the back of your intellect.