MediaConvert HLS subtitles off by default

According to https://docs.aws.amazon.com/mediaconvert/latest/ug/ttml-and-webvtt-output-captions.html

The captions track that you specify first in your job is signaled as the default track in the HLS manifest.

We're seeing our English subtitles automatically enabled on playback.

In the HLS manifest, I see

#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="English",DEFAULT=YES...

but manually changing that to

#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="English",DEFAULT=NO...

elicits the desired playback experience with subtitles turned off by default. I'm trying to find some way to achieve this through MediaConvert, rather than at the player level or as some post-processing job that modifies the manifest. Is there such a capability?