In your PROFILE :
1. Your USERNAME can never be changed. It’s only a name for your registration. The callsign on awards, toplists etc is not defined by this USERNAME
2. The PRIMARY callsign is the one used for all awards applying, toplists etc. Here you fill in the callsign you’re using most often, the one you like to see displayed on awards etc
3. The field “Other callsigns” is for your previous callsigns or extra callsigns still in use (like vanity calls etc)
3. For the countings ALL callsigns listed in PRIMARY and OTHER CALLSIGN fields are grouped. The total score is set on the PRIMARY CALLSIGN.