Unfortunately yes, currently the only way to change specialisation is a reroll. This may change in the future as BW do a lot of things we don't expect. Maybe end up as a consumable on the market knowing them
I was in the same boat as you. Assassin is awesome for PVE but I have always played ranged characters and personally being a sorceror made me look and feel more powerful. Even if in PVP I am a glass cannon without the cannon.
I rerolled my Assassin at 38 and remade him into a Sorceror.
Hope this helps.