This business about it being harder to relearn old habits. I'd like to state the case for the opposition.

Principle.        The ability to learn is like a muscle. The more you use it the stronger it gets. If you keep on learning stuff, learning more stuff becomes easier.

Observation.        Some people learn technical stuff up to a level where they can perform whatever type of music that motivates or interests them. This can be playing rhythm guitar, fingerpicking, lead electric, classical or whatever. Once they have reached this point the focus of their learning moves from technique to repertoire. If this move is 100% then their technique learning muscle will atrophy and eventually cease to exist.

Conclusion.        Only those people who have let their technique learning muscle atrophy to zero will experience difficulty in relearning old habits. For someone who is always developing technique, changing old habits is no harder than learning new material.