Custom preseed can be ordered?

Hello

Nowadays the customer faced issue that they can’t override proxy in yum.conf when they are deploying centos image.

After some investigation. I found out that below yaml is working ok.

Ubuntu Pastebin ( z_custom key )

I wanted to override this code which put by maas

https://github.com/maas/maas/blob/ff897252800a31ba83d3f7fbe4211ba44c1f2bb4/src/maasserver/preseed.py#L575

If ordering by this way is working, I think they can modify anything in their image.

and It would be better if this can be documented if it is true.

Thanks.