If you transform your set of functions into a package and install that package, then Julia will store a precompiled version of the package which is the one that is going to be “used” (with using). Thus, most of the functions will not get compiled again. Still there might be some functions of the package that need to be recompiled, if for some reason precompilation is not possible (see: Finding and fixing invalidations: now, everyone can help reduce time-to-first-plot).
But essentially only the script will be compiled, and not all the functions of your package, everytime.