Devoted Spirit is really the only one that's notably more powerful than the rest, and Desert Wind and Stone Dragon are the only ones arguably weaker than the rest. Letting the rest swap in and out probably will not affect balance in the slightest. Allowing a Swordsage to drop Desert Wind or anyone to drop Stone Dragon will slightly, but not massively, improve their power. Allowing non-Crusaders to get Devoted Spirit may potentially give them a fairly significant boost, I've heard, though I'm not familiar enough with the discipline to truly say.