If you have troubles changing your Commander name, you should know that the name you choose must:
- be unique (no two names are the same)
- pass the profanity filter (make sure your name is not vulgar/offensive)
- be written in the Latin alphabet, without any special characters or pauses after the last character
Keep in mind that in order to change your name you will be needing a Change Name item which costs 1 000 Gold and can be purchased from the Player Profile > Change Name Menu.