External drives are more prone to damage and failures, both because they’re more likely to be dropped/bumped/spilled on etc, and because of generally cheaper construction compared to internal drives. In the case of SSDs the difference might be negligible, but I suggest you at least make a copy on another “cold” external drive if the data is actually important
Not what you asked for, but you may be interested in getting a keyboard running QMK where you can define these kind of modifier overloading (and much much more) on the keyboard itself, so it’s “portable” and doesn’t require OS/DE settings