Adding to configuration parameters

Hi everyone,

I am transitioning my servers from CentOS to Debian. I noticed that
Debian is using a slightly different configuration scheme. Where CentOS
uses a single flat /etc/amavis/amavisd.conf-file where Debian uses
several /etc/amavis/conf.d/XX-whatever files and suggests, that all
changes are made to the file 50-user.

My quesion is, can I just extend configuration parameters that were set
in a previous file?

For example, in my CentOS-file, I have added some lines to the default
score_sender_maps. In Debian score_sender_maps is defined in
20-debian_defaults. Can I add lines to score_sender_maps in 50-user
without having to completely overwrite what was defined in
20-debian_defaults?

Thanks in advance
Julian