Shifting rune to change to an agile weapon?

Hey, friends!

I am playing a ninth level swashbuckler in the 2e Kingmaker AP. Because of some other feats I have requiring a free hand, I've been considering a shifting rune to change my rapier into something with the agile trait on turns where I have the action economy to do so. This would be most useful against groups of enemies, as I use a gain panache, finisher, move/regain panache gameplay loop against baddies with higher ACs.

As somebody relatively new to playing and not just listening to PF2E podcasts, I'd love to get some thoughts on if this is worth the gold/action economy investment or if I am better off looking at something more conventional.

FWIW, my rapier is currently +2, striking, and flaming.