As an example to configure a key mapping to add the tag 'to-do' and archive,
this is what I use:
-let g:notmuch_rb_custom_search_maps = {
+let g:notmuch_custom_search_maps = {
\ 't': 'search_tag("+to-do -inbox")',
\ }
-let g:notmuch_rb_custom_show_maps = {
+let g:notmuch_custom_show_maps = {
\ 't': 'show_tag("+to-do -inbox")',
\ }