charging wire frayed from physical torsion

In case you were wondering the outer conductor shields the ones within it, preventing electromagnetic radiation from causing interference with other devices. It's always twisted—wound in a sprial or braided for flexibility, and to prevent it from breaking too easily when subjected to repeated bends. So are the conductors within it; you just don't see them.

Your picture does not show that it's broken.

The failure was not due to torsion, just damage from having been run over by an office chair, a common affliction. Your repair is perfectly ok.

amazingeugene wrote:

would it be that much of a risk if I just shrink-tubed it after putting on some electrical tape?

You can certainly wrap it to make it last longer—

You can replace it—

Find the right power adapter and cable for your Mac notebook ...

Apple Portables: Troubleshooting MagSafe adapters - Apple ...

Power & Cables - Mac Accessories - Apple

About Apple's Power Adapter Replacement Program --- US Only

amazingeugene wrote:

this'd be considered relatively safe, right? I made sure I wrapped around a bit past the damaged are and far out to the sides.)

Yes,

you are simply providing insulation wrap that has failed— with no wrap the next thing to fail would the conducting wires themselves—this is what you are trying to avoid.

👍 It's a good repair.