My phone decided it was time for a new passcode, and three days after changing it I'm still incorrectly punching in my old one out of habit. I can tell that it's becoming easier to auto-pilot my new code, but it still takes multiple tries and it will be at least a few more days before I have a success rate like before.

Let's assume this concept is inherently true for most forms of behavior. Of course if you were to wake up early and exercise as a morning ritual it could become routine, habit forming, and now you're prone to doing it. We have been told to do X, Y, and Z because they are good habits to form.

But perhaps there are elements to X,Y,Z that are more pragmatic to instill as habit than the overall activity. Maybe a stronger habit to learn is to wake up early, and then choose from a set of activities, instead of only making it a priority to exercise. Maybe the reason for this is (as an example) when a better morning option suddenly becomes available...if the habit is exercise, you might be prone to not take the better option without expending extra consideration to make it happen, versus the person who has made only the act of being awake habitual.

This is the same type of wiring that prevents me from getting my phone passcode in as quickly as I did before changing it. The interesting thing is if you were to ask me my new code, I would immediately respond correctly. But pulling my phone out of my pocket and trying to get to the home screen is a different circumstance.

There is obviously something deeply scientific about the phenomena of repetition and habit. I was wondering if anyone had any philosophies or advice on the subject as it pertains to being more successful and failing less often.

Define "more successful" and "failing less often". I believe that in order to be more successful we need to fail multiple times, so it's interesting that you bring up these two points because I firmly believe they go hand in hand. We don't always get things right the first time or even the 100th time, some learn to adapt quicker than others, but failure is what breeds success. I think most of the top athletes, business people and generally the most successful people can say that without a doubt.

enhance strengths/minimize weaknesses.

maybe changing my phone passcode once a month could help streamline faster learning for something unrelated. if so, it would be a terrible decision not to.

I think also that it depends on how important the new password is in your life. It's not a matter of survival or of any really big importance, so maybe that's why it takes a bit longer. If for example entering the old password had any significant effect on your life, I think you'd learn the new one at a quicker rate, so I believe it depends on the significance of learning the new habit that play a role in how fast we accomplish it.