How can I apply a patch file to a Mac Ports app?
That sort of patch file is what macports refers to, however each patch would need to be in a separate file.

However this case is more complex as you need to patch two things as you have spotted.


Make the program compile and run under OSX which the current macport will have done. In this case this will include fixing the paths with debian in.
Add the extra changes you have in the patch.


As a first start I would note that each macport has a maintainer who can be seen in the result of port info abcde and I would contact them with the issue. If unfortunately there is no maintainer as is true here then it might be worth asking on the macports user mailing list if someone else could do the patch.