You are free to use, modify, adapt, copy, and redistribute this addon, including its code and textures, for personal or commercial projects. You may create derivative works and share your modified versions however you wish, as long as you credit the original creator,  and mention The original addon as the original add-on.

You may not use this addon or its assets to distribute malware, viruses, scams, or other malicious content, or falsely claim to be the original creator.

You may not sell or monetize this addon itself, or a minimally modified version of it, in a way that misleads people into paying for an add-on that is substantially the same as the original. In particular, simply changing, removing, or adding a small amount of content, textures, features, or other minor modifications does not make the add-on eligible to be sold as a separate paid product

However, this restriction does not apply to substantial derivative works that have been genuinely reworked or rebuilt. If you create a significantly different project based on this one, such as a major rework with substantial new code, systems, mechanics, models, textures, or other original content created by you, you may charge money for that project or use it in a commercial project. The price should be for your own substantial work and additions, not simply for access to the original 

You may not falsely advertise a modified version as being entirely your own creation or imply that i created or officially endorses your derivative work.

Aside from these restrictions, you are free to use this addon however you wish.