Few years later, it is again time to address some licensing issues and uncertainties related to re-using and modifying other creators content. Most importantly, I believe addon makers and users need to understand that the fact something is possible or easily available technically does not mean they really can take it and do whatever they like with it.
There are various aspects to consider, but before we go any further, I recommend and urge You to read the following link that details models released by BI for further modification so far for Arma 1. Note that none of the Arma 2 or Arma 2: Operation Arrowhead were released for addon makers to be used so far. I will be unable to comment any further until later next week but I will follow up this topic as soon as I can.
I believe Creative Commons provides very good overview of various types of author's rights and I believe it becomes important for addon makers to understand those rights so I made a short excerpt from CC website (all info is courtesy of Creative Commons, available under cc-by license) and I can tell BI is currently evaluating if CC+ style of license could be used for this addon making community:
Public Domain (Universal License)
The person who associated a work with this document has dedicated the work to the Commons by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law. Works under CC0 do not require attribution. When citing the work, you should not imply endorsement by the author.
This license lets others distribute, remix, tweak, and build upon your work, even commercially, as long as they credit you for the original creation. This is the most accommodating of licenses offered, in terms of what others can do with your works licensed under Attribution.
Attribution Share Alike
This license lets others remix, tweak, and build upon your work even for commercial reasons, as long as they credit you and license their new creations under the identical terms. This license is often compared to open source software licenses. All new works based on yours will carry the same license, so any derivatives will also allow commercial use.
Attribution No Derivatives
This license allows for redistribution, commercial and non-commercial, as long as it is passed along unchanged and in whole, with credit to you.
This license lets others remix, tweak, and build upon your work non-commercially, and although their new works must also acknowledge you and be non-commercial, they don’t have to license their derivative works on the same terms.
Attribution Non-Commercial Share Alike
This license lets others remix, tweak, and build upon your work non-commercially, as long as they credit you and license their new creations under the identical terms. Others can download and redistribute your work just like the by-nc-nd license, but they can also translate, make remixes, and produce new stories based on your work. All new work based on yours will carry the same license, so any derivatives will also be non-commercial in nature.
Attribution Non-Commercial No Derivatives
This license is the most restrictive of our six main licenses, allowing redistribution. This license is often called the “free advertising” license because it allows others to download your works and share them with others as long as they mention you and link back to you, but they can’t change them in any way or use them commercially.
Additonal Rights Under Custom Terms
CC+ is CC license + another own agreement. It is not a new license, but a facilitation of more permissions beyond any standard CC licenses.
(a bit side step, but this is also an interesting concept worth checking so I include it here for completeness):
The Framers of the U.S. Constitution understood that copyright was about balance — a trade-off between public and private gain, society-wide innovation and creative reward. In 1790, the U.S.’s first copyright law granted authors a monopoly right over their creations for 14 years, with the option of renewing that monopoly for another 14. We want to help restore that sense of balance — not through any change to the current laws — but by helping copyright holders who recognize a long copyright term’s limited benefit to voluntarily release that right after a shorter period.