Yes. When you create a new message, you can select a List(s) or use the quick search to find specific Subscribers.
You can send a message to multiple Lists and/or multiple Subscribers. The example below shows a message that will send to everyone in the High School List + Darren and Ben. ⬇️
You can also send a message to a few subscribers, or only part of a list by going to the Subscribers page > Select a List or "View All" Subscribers. From here, select the subscribers you want to text > Options > Send a message.