Any chance this can have a toggle if you do not want to use the "oath" your race has been given so that you instead mumble a non-descript oath? Or a custom oath?

It would be a shame to not be able to use the spell at all (or at least in public) simply because it comes with messaging that is not in character for a particular character.

From the spell's description: "The words of the Oath vary, but always the intent is the same: a promise of swift and lethal violence to those who would defile that which the Ranger holds dear."