The Mystic is an Unearthed Arcana class in D&D 5th Edition. All the Mystic Orders (subclasses) except the Soul Knife get Bonus Disciplines :
At 1st level, you learn two additional psionic disciplines of your choice. They must be chosen from among [your Order’s] disciplines.
Regular disciplines can be swapped out :
In addition, whenever you gain a level in this class, you can replace one discipline you know with a different one of your choice.
Can the Bonus Disciplines also be swapped out, even for replacements that aren’t from the Order ?