It's really boring when all the prefixes can basically only be bought, although it would be more interesting if they could be obtained for achievements on the server like:
[CubeVeteran I] - for reaching level 50
[CubeVeteran II] - for reaching level 150
[CubeVeteran III] - for reaching level 250
Also you can add chests as it's made on java that appear every 3 hours and with a 15% chance they can drop the [Explorer] prefix or
with a 50% chance - 10 xp
and with a 35% chance nothing