I could not understand what you want to do, so I want to give advice that you cannot use INSendMessageIntent outside your capabilities. This means that you must use some keywords for your custom sentences to make Siri understand your custom command for INSendMessageIntent.
After creating the AppIntentVocabulary.plist file , it must be sent to the Apple Siri Servers . You can achieve this by changing your Siri iPhone to another that you know, and then use the simple siri messaging process with that language.
Then change it again to the desired language.
Do this every time you change AppIntentVocabulary.plist.
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