You certainly could, but it would be better not to.
There are first of all correspondences - certain days of the week and phases of the moon will be good for a break-up spell and others which will be good for bring a person back. You don't need to do things on the best day or under the most favorable moon, but it helps and if it's the right day and phase for one, it's definitely not right for the other.
The other issue to take into consideration is your own energy and mind. After generating and focusing energy toward breaking people up you will be very psychically and energetically flooded with that specific kind of charge. You can ground and banish and cleanse to help flush it out, but even on a purely psychological level you generally can't just switch gears like that. You could try casting another spell after, but it would be almost as if your mind and energy would contaminate it.