Is there a possibility to literally override a target or emulate this somehow?
So, when I call
See the "Target overriding" section of the import task or the "Target rewriting" section of the include task. In short, give the common build.xml a project name like "common", and then use "common.release" in the antcall.
I'll note that antcall isn't quite the same since it starts a new project at runtime, which means variables set by the target won't be visible later. I don't have Ant available on this machine to test, but you might try something like this to avoid the antcall:
<target name="release" depends="common.release, -post-release"/>