SunnyD,
For me, it depends on how many points you want to spend in the souls. Myself, I focus on only 2 souls, with the 3rd as just filler.
Because of that, my tank for example is a Paladin + Warlord + Beastmaster. The beastmaster is my filler class. I will not put points into it and will focus only on Paladin and Warlord. But the beastmaster has a pet, so it's free DPS that is passive, and better than any other choice (imho).
My Rogue is the same. I have a Ranger/Saboteur/Bard. I am not going to put points into the Ranger, but its a free pet and free DPS. I have 80% of my points into Bard, the rest in Sabo.
That said, if you need to change out souls, all you need to do is go to the trainer, spend some money, reset your points. When they are all 0, you can swap out souls in your role. So if you did not put points into Riftblade, all you need to do is complete the rift quests to get new souls, and then click the icon on the soul screen and swap out the Riftblade for a Marksman, and you don't have to create a new role or recreate your character.
To make a long story short, as long as you have spend 0 points into your soul, you can swap them out as long as your character possess the souls to begin with.