These things are already possible.

For desynthesis, while I guess you can't actually just reset the skill back to 1, you don't need to. Just start leveling whatever skill you decided you'd rather level and if you hit the 300 mark it will start removing points form the others. If you are planning on using all 300 skill points and not in the class that's already leveled, then there is a tedious workaround right now and I believe they've said they are planning to make it more obvious and less tedious to keep a particular skill leveled. This still wouldn't reset your unwanted class, but making the others unable to delevel would be just as good.

I don't know the exact process, but the NPC who gives you the sphere scroll mentions removing materia for you if you make a mistake or change your mind. Others might have a more detailed answer for you there, but having just started my Novus I recall that it is an option.