The controller's tools can set an assignment's settings

Per-machine and mesh-wide settings could be set only from the
controller's command line. The settings verb runs settings set|clear,
passing the values inline, which the command now accepts as well as a
file (novox/hq issue 198).

internal/catalogue/verbs.go

@@ -136,6 +136,15 @@ var ControllerVerbs = []Verb{
 			"node":   "the machine that runs the module",
 			"module": "the module's name",
 		}, []string{"node", "module"})},
+	{Name: "settings", Description: "Set what an assignment is configured with: a module's settings for the whole mesh, " +
+		"or for one machine. Replaces that layer whole — what it does not name, it no longer sets — and takes effect " +
+		"at the next push. With clear, removes the layer and the module is back to what its definition says.",
+		Input: schema(map[string]string{
+			"module": "the module's name",
+			"values": "the settings as a JSON object, for set",
+			"node":   "one machine; the whole mesh when absent",
+			"clear":  "\"true\" to remove the layer instead of setting it",
+		}, []string{"module"})},
 	{Name: "build", Description: "Have the build machine build a repository. Answers at once with the build's id: " +
 		"`builds` with that id follows it line by line, and the module is registered when the outcome comes.",
 		Input: schema(map[string]string{