In Report Options of Balance (with >>eguile<<) in General (Bearbeiten >> Berichtsoptionen >> Allgemein) the Report title can be changed. The saved new title appears in ~/.gnucash/saved-reports-2.4 but it does not appear in the report itself. The title remains "Bilanz (mit >>eguile<<)". [Fedora release 27]
This is confirmed, and fixed in repository. The "Report name" option will be used to set the report title.