Is it safe to correct sources.list

I was wondering what’s the correct surocers.list.
My current sources.list is the default one that comes with VM an looks like this:

deb http://cdn.debian.net/debian/ wheezy main
deb-src http://cdn.debian.net/debian/ wheezy main

deb http://security.debian.org/ wheezy/updates main
deb-src http://security.debian.org/ wheezy/updates main

# wheezy-updates, previously known as 'volatile'
deb http://cdn.debian.net/debian/ wheezy-updates main
deb http://mirrors.neusoft.edu.cn/mariadb/repo/5.5/debian wheezy main
deb-src http://mirrors.neusoft.edu.cn/mariadb/repo/5.5/debian wheezy main
deb-src http://cdn.debian.net/debian/ wheezy-updates main

but when I apt-get update there are errors:

Err http://mirrors.neusoft.edu.cn wheezy/main Sources
  500  Internal Server Error
Err http://mirrors.neusoft.edu.cn wheezy/main i386 Packages
  500  Internal Server Error
Fetched 16.7 MB in 17s (934 kB/s)
W: Failed to fetch http://mirrors.neusoft.edu.cn/mariadb/repo/5.5/debian/dists/wheezy/main/source/Sources  500  Internal Server Error

W: Failed to fetch http://mirrors.neusoft.edu.cn/mariadb/repo/5.5/debian/dists/wheezy/main/binary-i386/Packages  500  Internal Server Error

E: Some index files failed to download. They have been ignored, or old ones used instead.
root@erpnext-vm:~#

Is it safe to correct the sources.list and, for that matter, is it safe to update Debian?

Should we include

deb http://mirror.timeweb.ru/mariadb/repo/5.5/debian wheezy main
deb-src http://mirror.timeweb.ru/mariadb/repo/5.5/debian wheezy main

instead of

deb http://mirrors.neusoft.edu.cn/mariadb/repo/5.5/debian wheezy main
deb-src http://mirrors.neusoft.edu.cn/mariadb/repo/5.5/debian wheezy main

( as suggested here: https://downloads.mariadb.org/mariadb/repositories/#mirror=timeweb&distro=Debian&distro_release=wheezy--wheezy&version=5.5 )
and enable contrib and non-free repositories

so that the sources.list looks like this:

deb http://ftp.de.debian.org/debian/ wheezy main contrib non-free
deb-src http://ftp.de.debian.org/debian/ wheezy main contrib non-free

deb http://security.debian.org/ wheezy/updates main contrib non-free
deb-src http://security.debian.org/ wheezy/updates main contrib non-free

# wheezy-updates, previously known as 'volatile'
deb http://ftp.de.debian.org/debian/ wheezy-updates main contrib non-free
deb-src http://ftp.de.debian.org/debian/ wheezy-updates main contrib non-free

# deb http://mirrors.neusoft.edu.cn/mariadb/repo/5.5/debian wheezy main
# deb-src http://mirrors.neusoft.edu.cn/mariadb/repo/5.5/debian wheezy main
deb http://mirror.timeweb.ru/mariadb/repo/5.5/debian wheezy main
deb-src http://mirror.timeweb.ru/mariadb/repo/5.5/debian wheezy main

So…no answer?
bump

I changed my sources.list (for Debian Wheezy) for mariadb to get downloaded and installed.
I installed mariadb from other mirror repository.
It works. Only thing is if script is used it might add sources again and try to install mariadb, yet mariadb being already installed it’ll go ahead with further steps.

Many distros officially added mariadb into their repos.