+ Grob *gr = unsmob_grob (grob);
+ SCM_ASSERT_TYPE (gr, grob, SCM_ARG1, __FUNCTION__, "Grob");
+ SCM_ASSERT_TYPE (scm_list_p (tweak) == SCM_BOOL_T
+ && ly_is_procedure (scm_car (tweak)),
+ tweak, SCM_ARG2, __FUNCTION__, "Tweak");
+
+ global_registry_->replace_grob_tweak (gr, tweak);