If you want to stop automatic emails from being sent when manually updating a registrations' custom status on the backend, this can be managed through the advanced logic rule configuration. 

Steps to update the Settings:
1. Edit the Custom Status -  Go to Plan > Event Setup > Custom Status and select the custom status you want to adjust by clicking on the pencil icon.

2. Click on the Advanced button - located at the lower-left corner of the page. 

3. Modify the Logic Rule - Click on the edit or pencil icon in the advanced logic rule setting, uncheck the option labeled Send Email to Registrant email

4. Save your changes - Once updated, click Save to apply the new configuration. 

Additional note: 
Disabling the "Send Email to Registrant Email" option will affect all instances where this custom registration status is used — including forms. This means that no email will be sent to customers when the status is applied through any form.