Is it possible to replace my username in Terminal with special characters?
The PS1 prompt is defined in /etc/bashrc and the default is usually PS1='\h:\W \u\$ '. You'd replace the \u with *****. You could also just add, e.g export PS1='\h:\W *****\$ ' to your ~/.bash_profile file, while leaving the system file (/etc/bashrc) alone.