Yes and no. The scripts are open source under the GPL ver3 license and you can use or modify them to your heart's content. The images, however, we bought or created for Midnight Sun and they may not be used elsewhere. The only exception are avatars - those in the Allavatars directory come from allavatars.com and you should download them from there. The rest of the avatars are from images that are public domain.
All the scripts are accessible under the Scripts menu of Mudlet and can be freely edited from there. The layout is created in Geyser and the scripts are written in Lua. With a little bit of patience and scripting knowledge you can modify the GUI to suit your needs. Don't forget to keep a backup of the package, so that it does not get overwritten if we upload an update to the official version.
When we released the current version, we did have a few things that did not make it in, such as guild-specific information. So far other, more pressing tasks have kept us from working on it. It is not a small project to add guild support - not only on the client side, we also have to modify our mudlib to be able to send the necessary information. So yes, there most likely will be another version, but at the moment there is no estimated deadline. It is just something that we want to return to when time allows.