
AdamB.47749 (Customer) asked a question.
We need to use the same custom email domain for Okta emails across multiple Okta orgs. I see in the DNS settings the only difference between the 2 orgs is the TXT field. The domain is already tied to Org 1, if I go and change my DNS settings to accept the TXT from Org 2 does it automatically invalidate the custom email domain for Org 1?

Unfortunately, this is would not be possible to achieve. You can only use one email domain at a time. As per doc here or the link below. For the second tenant, you will need to use a completely different email domain.
Custom email domain
https://developer.okta.com/docs/guides/email-customization/configure-custom-email-domain/