Ahhhh!!! : "Update project version in all *.xml; *.sh; *.bat files manually. E.g. replace 3.3.1-SNAPSHOT with 3.3.1.BETA1"
Actually I've just replaced the version number in the pom.xml of the sub project "menu-component": it was "3.3.3.Final" and I've put "3.3.3.custom".
Then I have compiled only the "menu-component" (with my modifications).
Then I have modified my project pom to exclude menu-compoment dependency in the richfaces-ui dependency. And I have added the dependency menu-component with my "3.3.3.custom" version.
And it worked well.
Thanks again for your answer.
For info: the bug in the menu.js only happens when the items all have a sub-menu. Which can't be tested on the Exadel demo because this case does not exist.
The problem is that a mouseover event on an item that does have itself a submenu, immediatly closes the previously opened sub-menu without any closing timeout consideration!