openarc.org provides infrastructure you may use to get familar with ARC.
Send a message to firstname.lastname@example.org. You'll receive a response instantly. This response contain the message as received by the service. This allowes you to inspect how OpenARC validate your sent message.
Send a message to email@example.com. You'll receive your message /forwarded/ back to you. It's not a new one. Ususally existing DKIM signatures should still intact after forwarding.
But you may force the broken DKIM signatures. Place the text "modify" somewhere in the Subject and it will be replaced with "modified" on forwarding. Your DKIM signature
will be no longer valid. (we assume you sign the RFC5322.Subject header as suggested by RFC...)