Okay, --resource META-INF/my_file.txt almost did it. Except it becomes META-x45INF/my_file.txt in the jar. Apparently that’s because the dash is being escaped:
Okay, I made a maven plugin which makes maven call the haxe compiler to produce the required bytecodes. (Normally maven calls the java compiler)
In that case I am able to make use of the entire maven build tool, including resource bundling mentioned in the OP. So I would say the problem is solved for now.