Modified co-sleeping in itself is a very flexible term, and knowing when and how to stop modified co-sleeping is just as flexible. Simply put, it will look differently for each family, just like modified co-sleeping never looks the quite the same from one family to the next.
The term has a pretty fluid definition, but it essentially means any form of co-sleeping that works for your family. It can be room sharing, where your baby sleeps in a crib next to your bed. It can be sharing a bed with your child, or letting them sleep in a bassinet co-sleeper that attaches to your bed. In short, it's making co-sleeping work for you.
When you and your child feel it's time to stop, the process can be just as flexible. Maybe you've decided to take back your room for yourself and move your child into a toddler bed in their own room. In that case, the Baby Sleep Site suggests taking it slowly. You can begin by transitioning them out of your bed and into their new bed (still in your room, but just in a separate bed.) Then, after a while, move the party into their room, where you'll sleep with them for a few nights (or however long it takes till you think they're ready.) Eventually, the goal is that they'll be ready and even excited to sleep in their very own room.
If you're not quite ready to end the room sharing portion, but just want them out of your bed, the process is even simpler. What To Expect suggested that parents simply move their baby into a crib, toddler bed, or bedside co-sleeper, keeping it an arms length away. You'll still be able to reach your baby, should they miss the closeness, but they'll gradually get used to sleeping in their own space as well.
Whatever situation you're in, don't expect modified co-sleeping to end in one night. Whether you've been co-sleeping since the beginning or moved your baby to your room out of desperation for better sleep, the transition out should be taken slowly. Embrace the transition though, because before you know it, your little one will be in their own room sleeping through the night.