MySQL datadir and systemd

It seems to be getting harder and harder to move the mysql database directory (datadir). A few releases back, apparmor came in the picture and I had to remember to go into /etc/apparmor.d/usr.sbin.mysqld and change the datadir there so mysql was allowed to use the new directory.

Now with systemd there is apparently a script I have to modify. In order to get mysql to start I had to edit /usr/share/mysql/mysql-systemd-start and change the tests for the database directory to use the new directory.

This seems like a clumsy way to go about this, so I'm wondering if there is some command that does this change for me. What is the recommended way to tell systemd where to look for the mysql database directory?