Specify content of data sent for URL destinations

I was looking at trying to use HamAlert to post spots to the social networking service, Mastodon. I know that Mastodon can accept web requests of the application/x-www-form-urlencoded variety. However, if I am understanding the HamAlert URL notifications feature correctly, HamAlert sends all available parameters in the web request. Also, Mastodon expects the text of a status update to be preceded by status=

Would it be possible instead to be able to provide a custom format for the data that is sent? Perhaps specifying the text and the included parameters? For example:

status=<<<fullCallsign>>> was spotted at <<<frequency>>> by <<<spotter>>>