Hi, @alex-vdb. Let me share some insights about auto email settings for credit memos in QuickBooks Online. The option to automatically change the email settings in QBO is not yet possible. You can still edit it every time you'll send a credit memo.
After clicking on Save and Send, you can edit the Subject line but changing the company name is unavailable in QBO. You can also send suggestions to our developer's team. This way, they can include it in the next updates. Here's how:
Select the Gear icon at the top, then Feedback.
Enter your comments or product suggestions, then select Next.
To find all the ways you can customize invoices and email messages, I recommend checking out the following article: Customize invoices, estimates, and sales receipts in QuickBooks Online.
If you need further assistance with credit memos in QBO, please leave a response below. I'm always here to help. Have a good one.