You can define in seahub_settings.py what filetypes should be read only and which one can be edited:
ONLYOFFICE_FILE_EXTENSION = ('doc', 'docx', 'ppt', 'pptx', 'xls', 'xlsx', 'odt', 'fodt', 'odp', 'fodp', 'ods', 'fods')
ONLYOFFICE_EDIT_FILE_EXTENSION = ('docx', 'pptx', 'xlsx')
ONLYOFFICE_FILE_EXTENSION = read only
ONLYOFFICE_EDIT_FILE_EXTENSION = editable
But be careful some (or all?) filetypes (like .ods) will be converted into XML-format, and it’s therefore not recommended to allow editing for LibreOffice files (see Onlyoffice corrupts .odt)