Although the documents don't describe product branding, it seems to be
supported with a "product" property, which I had properly set in my
build.properties. Unfortunately, during packaging I get
java.io.EOFException from eclipse.brand task located in generated
assemble.<my.feature>.win32.win32.x86.xml script. This seems to be
caused by the fact that eclipse.exe is not copied to the target
directory (set in root attribute of the task) before the task is executed.
I guess I could just copy it there in one of the customTargets.xml
targets, but I believe there's already some infrastructure for that in
the org.eclipse.releng.basebuilder itself.
In particular packaging.properties files that I found in
org.eclipse.releng.eclipsebuilder project seem to leverage that
infrastructure. Unfortunately I couldn't find any documentation about
how to setup it in existing customTargets.xml.