I don't remember if respeccing your skill was available in-game or if it came with a patch but if not, make sure to get a mod that offers this. It will make it less roleplay-ish but at least you don't have to worry you will get stuck because you picked a skill that had a good description but poor design.
Other than thatand some Fixpack you are good to go.
Well, in the expansion is possible to do it.
In the first OC is not possible to do it. Yet, as long you focus on a single specialization for rogue and warrior, you are not wasting skills, and even then, is feasible to finish the OC. Once the expansion begins, you can re-scope your character.
For casters, as long you finish your line (the four spell in a single row), should be enough. The game will give you a healer and a "dark user". So, you can experiment a little more in any other row.