Hello Sven,
The "addpath" command is only a small part of getting the custom messages working with MATLAB. It is required to register the generated M-files with MATLAB, but the libraries that get built are registered in a different way as part of the "rosgenmsg" run.
In R2020b, if you run rosgenmsg on a custom message folder, and then re-run it without changing anything, it shouldn't actually build the messages a second time. A quick check is done (on a package-by-package basis) to see if the message definitions have changed, and if not, they are simply re-registered to MATLAB.
You can take advantage of this to transfer pre-built packages between computers. Be aware that it only works when built by the same MATLAB version and on the same computer architecture (OS). If your folder structure looks like this:
custom_interfaces/
|-matlab_msg_gen_ros1/
|-package_1_msgs/
| `-msg/
| `-MyMsg.msg
`-package_2_msgs/
`-msg/
`-MyMsg2.msg
then transfer the full "custom_interfaces" folder to the other machine and run "rosgenmsg" on that folder. It won't work if the generated folder name changes from "matlab_msg_gen_ros1", as that will make it appear that messages have not been generated at all.
-Cam
