patching a Debian installation package

  1. Unpack the deb file in question.

    dpkg-deb -x slack-desktop-LATEST-VERSION-PLATFORM.deb unpack

    dpkg-deb --control slack-desktop-LATEST-VERSION-PLATFORM.deb unpack/DEBIAN

  2. Edit the file named control and replace the unsupported library with a supported version/alternative

    libappindicator3-1 -> libayatana-appindicator3-1

  3. Repackage the contents of the folder unpack along with the updated control file

    dpkg -b unpack slack-desktop-LATEST-VERSION-PLATFORM-PATCHED.deb

  4. Install as usual

    dpkg -i slack-desktop-LATEST-VERSION-PLATFORM-PATCHED.deb