Yes; currently the header line is defined like this in sphinx.sty:
\fancyhf{}
\fancyfoot[LE,RO]{{\py@HeaderFamily\thepage}}
\fancyfoot[LO]{{\py@HeaderFamily\nouppercase{\rightmark}}}
\fancyfoot[RE]{{\py@HeaderFamily\nouppercase{\leftmark}}}
\fancyhead[LE,RO]{{\py@HeaderFamily \@title, \py@release}}
You can customize this is latex_elements['preamble'] by using
these commands again (between \makeatletter and \makeatother).
Georg