I do this if I'm just out of energy and feeling super done with stuttering. Sometimes you gotta be pragmatic and I don't think anyone can judge us for that. One of the things about having a condition like this is you need to prioritise your mental health sometimes, which can mean avoiding stuttering, which can mean changing what we say. That being said, sometimes saying 'I don't know' or not talking at all is better than being false. You can even explain to people that you're too tired to talk for the rest of today or something. I'm not against the occasional disingenuousness but it can reflect badly on you if it becomes a habit, and it really screws with your sense of self (I once had a crisis where I didn't really know who my authentic self was because I was changing how I communicated so much).