PackageCompiler image validity

As advised by several here, I built a PackageCompiler image for Plots,GR to alleviate the time-to-first-plot problem. I notice that when I start Julia using -J path/to/sys.dll, I end up in a dedicated environment (PackagesPrecompile).

My question is: what package management actions am I still allowed without rendering the image invalid? I assume I should not do anything that changes the versions of the compiled packages and their dependencies. Does that leave any safe operations? In particular can I safely add packages to this environment?