Regarding whether a username can be changed or not, firstly would depend whether or not you have already updated your username upon purchasing the spellbook (starter pack) for your account, or if you have already registered your Splinterlands account by using an already active Hive account.
Users who initially register an account on the Splinterlands website (excluding with a Hive account), called a lite account, will start with a default name for a lite account, such as a few of the examples listed below:
The names and numbers all vary for each user and provide a unique username until a user does decide to activate some of the main features of a Splinterlands account such as the ability to start earning rewards for their play by purchasing the spellbook for this lite account. Upon activation, you should be able to enter a new username to replace the default username that an account had initially been given. This username change would then become irreversible, as this action also at the same time opens a static Hive address, which doubles as both a deposit address for receiving and storing Hive assets, which includes Splinterlands assets, and your permanent username.
Your Hive address cannot be changed, though can be utilized as a username along with your private keys throughout various Hive websites and applications, such as in peakmonsters.com, baronstoolbox.com, and Hive Keychain. In order to claim your private keys for your account, just click on your username (or the shield icon), and then click on the "Request account keys" option, which should allow you the option to retrieve your Hive account's private keys by having them delivered via email.
If you want to learn a safe way on how to manage your keys with Hive Keychain for logins and initiating transactions, or find you are having troubles with claiming your Hive account's keys please follow the either of the corresponding guides below:
This concludes the guide discussing changes to player usernames.