How I can create another username having different appearance with my main blog?

You can make 2 accounts with two different browsers & two different webcams. But please note that there could be issues while you’re trying to broadcast from the two accounts at the same time. This can & does cause some broadcasters to be banned.

It would be best to ask Support that you want to do this & ask them for some guidance on doing this. You’ll then have the messages from support to back up yourself if you do get banned.