How to modify ros-launch file?

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Hello, I'm using ROS kinetic on Ubuntu 16.04.

I've ever modified existing ROS-launch files some times, but all I did was to change the parameter's name or values.

This time I want to add another node into the launch file, and I'm pretty wondering above whether I have to modify CMakelist.txt or any other files to make sure I'll use another node.

Is it OK if I add some lines into the launch file without any modification on the files kinds of CMakelist.txt?

And also, can I include a node which is in another workspace? I mean,

<include file="$(find A DIRECTORY FROM ANOTHER WORKSPACE)/THE_LAUNCHFILE.launch" >

is the above OK?

Thanks in advance :)