Updated Notify_Custom_JSON (markdown)

Notify_Custom_JSON.md

@@ -52,6 +52,29 @@ Send a JSON notification to our web server listening on port 80:
 apprise json://json.server.local
 ```
 
+### Payload Manipulation
+Making use of the `:` on the Apprise URL allows you to alter and add to the content posted upstream to a remote server.
+
+```bash
+# Add to the payload delivered to the remote server as if it was part
+# the prepared message Apprise would have otherwise put together
+#
+# Assuming our {hostname} is localhost
+# Assuming we want to include "sound": "oceanwave" as part of the existing payload:
+apprise -vv -t "Test Message Title" -b "Test Message Body" \
+   "json://localhost/?:sound=oceanwave"
+```
+
+The above would post a message such as:
+```json
+{
+   "version": "1.0",
+   "title": "Test Message Title",
+   "message": "Test Message Body",
+   "type": "info",
+   "sound": "oceanwave"
+}
+
 ### Header Manipulation
 Some users may require special HTTP headers to be present when they post their data to their server.  This can be accomplished by just sticking a plus symbol (**+**) in front of any parameter you specify on your URL string.
 ```bash