According to the LyX wiki and other sources I can use \renamecommand{\abstractname}{Summary} without an \addto if I remove (or deactivate) the babel package.
The document class is KOMA-script Report. Under Tools -> Preferences -> Language Settings -> Language I changed 'Default' to 'English' and Language Package to 'None.' When I try to compile the document for a preview now I get an error: Undefined control sequence. Missing \begin{document} and the command was never def'd. What simple thing have I missed here? TIA, Rich