DKIM with alternate domain (ClickTracking.CustomDomain and MailSettings.BounceDomain ?)

[TrendyTim]

I am trying to support an alternate sending domain, but sendgrid is using the wrong DKIM, i've been told i need to use this json in the api request
(admittedly it was ChatGPT that told me, but sendgrid docs directly are not helping in the slightest, im not sure if its all thats required but its all ive got)

{
"mail_settings": {
"bounce_domain": "yourdomain.com"
},
"tracking_settings": {
"click_tracking": {
"enable": true,
"enable_text": true,
"custom_domain": "click.yourdomain.com"
}
}

but the sdk doesn't let us provide that information, and id prefer not to have to resort to a raw api call.

Is there any chance of adding the bounce_domain and custom_domain, was there a reason it was never added in the first place with the rest of the options that i'm not aware of (or if anyone has got a better solution I'm all ears) ?

Thanks