mixins

src/my/mixins/skip.mixin:

{
  "build": {
    "skip": {
      "packages-skip": ["foo1",
                        "foo2",
                        "bar",
                        ],
    }
  }
}

src/my/mixins/index.yaml:

mixin:
    - skip.mixin

Then:

colcon mixin add skip file://`pwd`/src/my/mixins/index.yaml
colcon mixin update skip
fetching links: file:///home/lucasw/ros2_ws/src/my/mixins/index.yaml ...
  fetching file:///home/lucasw/ros2_ws/src/my/mixins/skip.mixin ...
  * /home/lucasw/.colcon/mixin/skip/skip.mixin

And run update if the index or mixin file/s change, and build with

colcon build --mixin skip

mixins

src/my/mixins/skip.mixin:

{
  "build": {
    "skip": {
      "packages-skip": ["foo1",
                        "foo2",
                        "bar",
                        ],
    }
  }
}

src/my/mixins/index.yaml:

mixin:
    - skip.mixin

Then:

colcon mixin add skip file://`pwd`/src/my/mixins/index.yaml
colcon mixin update skip
fetching links: file:///home/lucasw/ros2_ws/src/my/mixins/index.yaml ...
  fetching file:///home/lucasw/ros2_ws/src/my/mixins/skip.mixin ...
  * /home/lucasw/.colcon/mixin/skip/skip.mixin

And run update if the index or mixin file/s change, and build with

colcon build --mixin skip

mixins

sudo apt install python3-colcon-mixin

src/my/mixins/skip.mixin:

{
  "build": {
    "skip": {
      "packages-skip": ["foo1",
                        "foo2",
                        "bar",
                        ],
    }
  }
}

src/my/mixins/index.yaml:

mixin:
    - skip.mixin

Then:

colcon mixin add skip file://`pwd`/src/my/mixins/index.yaml
colcon mixin update skip
fetching links: file:///home/lucasw/ros2_ws/src/my/mixins/index.yaml ...
  fetching file:///home/lucasw/ros2_ws/src/my/mixins/skip.mixin ...
  * /home/lucasw/.colcon/mixin/skip/skip.mixin

And run update if the index or mixin file/s change, and build with

colcon build --mixin skip

More on colcon mixins: https://github.com/colcon/colcon-mixin-repository