As the editable templates were not supported in AEM SPA archetype in 6.4.3. But with the release if AEM 6.5.3 we have editable templates available for AEM SPA architecture.
Untill you migrate to AEM 6.5.3 you don't get editable template as part of SPA, but you can manually edit the policy at /conf/wknd-events/settings/wcm/policies/wcm/foundation/components/responsivegrid/default