Only use a custom www subdomain. Not the appex domain

I would like to use the www.imec.be subdomain for imecbe.netlify.app, but not the appex domain imec.be.

If I understand this question correctly this requires manual intervention from the netlify support team?
Could this be applied to my site aswell?

What are the implications for this concerning the automatic TLS certificate? Will this still work?
Will the certificate work if I configure the CNAME for www.imec.be right now? Or do I have to wait for your intervention first?

The site is receiving quite a bit of traffic so I would like to minimize downtime as much as possible.

Thanks a lot for any help!

Hey @dmerckx,
The main intervention from our side is around the TLS certificate. When you add a custom domain to a site, we automatically create a cert the covers the apex domain and any subdomains you’ve added. So this change will require us to create a new cert for you, with the apex domain removed.

It looks like your DNS records for that subdomain are not currently pointing to Netlify, and we will need that in place before the certificate can be provisioned. Alternatively, you could bring a custom certificate. In that case, I would think that you could just configure the CNAME right now and it would work… but you would probably want to test!

Please let us know if you have any questions or want to move forward with only the subdomain pointing to Netlify.