As @ajduplessis says, your grip will change during your shave. It just comes naturally as you concentrate on angle , pressure (or lack of) and stroke direction. I also often change the angle between blade and scales during a shave. About ⅔ of my shave is done with the scales at about 180°.
I don’t like the idea of practicing with a dull or a taped edge. In theory it sounds alright, in practice it is inviting you to develop bad habits.
Part of the process of becoming competent with a straight razor is nicking yourself...these little nicks and cuts let you know that you did something wrong, and to adjust fire on your technique. If you use a dull or taped edge, you lose that, and almost assuredly will make the learning process more lengthy and arduous.