Combine write into one command so you can do both simultaneously.

main.go

@@ -52,16 +52,12 @@ var cli struct {
 		Bucket string `help:"Remote bucket"`
 	} `cmd:"" help:"Fetch one tile from a local or remote archive and output on stdout."`
 
-	WriteHeader struct {
+	Write struct {
 		Input          string `arg:"" help:"Input archive file." type:"existingfile"`
-		HeaderJsonFile string `arg:"" help:"Input header JSON (written by show --header-json)." type:"existingfile"`
-	} `cmd:"" help:"Write header data to an existing archive in-place."`
-
-	WriteMetadata struct {
-		Input        string `arg:"" help:"Input archive file." type:"existingfile"`
-		MetadataFile string `arg:"" help:"Input metadata JSON." type:"existingfile"`
+		HeaderJson string `help:"Input header JSON file (written by show --header-json)." type:"existingfile"`
+		MetadataFile string `help:"Input metadata JSON (written by show --metadata)." type:"existingfile"`
 		Tmpdir       string `help:"An optional path to a folder for tmp data." type:"existingdir"`
-	} `cmd:"" help:"Write JSON metadata to an existing archive in-place."`
+	} `cmd:"" help:"Write header data or metadata to an existing archive."`
 
 	Extract struct {
 		Input           string  `arg:"" help:"Input local or remote archive."`