You can't do that for Colonial Nations in the new world. If they go free then you annex them, they just because a Colonial Nation again. You can't ever own real, controlled land in the New World, and you can't Release a normal Vassal from the New World. So you'd gain nothing by the whole process of freeing them and conquering them again; you should just beat them when their Liberty Desire reaches the Independence point, that will lower it again (for a while.)
You can. You just can't own real, controlled land if it is 5 or more contiguous colonies. Of course, if you have the DLC enabled, it seems rather pointless do so and that gives me hope that the AI will seek to colonise in a more contiguous pattern as opposed to now where say Spain drops colonies here and there along the east coast of the Americas before filling it out (ergo, hopefully no more Spanish Canada in most cases).