Yes. If you open the group conversation and hit the person button/icon at the top, it will give you a dialog with a list of users. One of the buttons on this dialog is Edit Recipients.
Using that option will populate the current groups contacts into the compose screen. From there, you can remove or add contacts. When you are done, hitting the next button will start a conversation with the selected contacts.
Group MMS doesn't allow you to directly edit the recipients in a group message, so the only thing that Pulse SMS can do is start a brand new conversation.
