They've already tracked down the original license holders/issuers in order to release the software in the first place. It seems to me like it would be orders o

They've already tracked down the original license holders/issuers in order to release the software in the first place. It seems to me like it would be orders of magnitude less work to contact a source port author and get all parties to agree to a simple modified license that would allow for source modifications to be included in the bundle. (The original Parallax license for Descent, as well as the Rebirth modification to it, can be found at https://github.com/CDarrow/DXX-Retro/blob/master/COPYING.txt https://github.com/CDarrow/DXX-Retro/blob/master/COPYING.txt . I'm not sure it would even need to be modified -- it prohibits "end users" from using it for revenue-generating purposes, but doesn't prohibit the original rights holders from bundling that end-user code with the original software.)