Hey @jvail! Apologies for the delay in responding to your message here!
I'm not sure I have 100% parsed your question properly. It seems you have set up magick as an ExternalPackage in the /etc/rstudio-connect/rstudio-connect.gcfg file?
In order to do that, you need to install magick into every R version installed on your RStudio Connect server. Typically this is done by "assuming root" (sudo su) and then installing the package.
Once that is done, you shouldn't have to do anything else! Just publish as usual, and Connect will "ignore" installing magick when it is rebuilding an app environment. Please keep in mind that this means all content for any given version of R will use the exact same version of the package. Further, changing that version will simultaneously affect all content using that R version.
Do you mind saying a bit more about why you are installing magick as an external package? Has it been a trouble to install?
Did I understand your question properly?