In liberty online, there were many ways a player could get a subclass, but the best way to get a suitable subclass was by performing well in the trial temple at the time of tier-up.
The tier-up was more like advancing to the next stage of evolution. Tier 0 and Tier 1 players were just in a completely different power class.
There were only a few players in his last life that were able to tier up above Tier 3. That was the limit and end of the power-up progress of the bad-skill player.
Many players in his last life got the chance to select the sub-class based on their performance in the trial.
A player was bound to select only one sub-class in the game. Although he could change that sub-class later on, that would mean he lost some permanent features of the sub-class.