You can update anything within the same minecraft version and it will be fine. i have updated and down dated forge many times and my modpack server world is working even though i have down dated forge and mods.
You can update your forge by downloading the latest universal build and placing that in your BIN folder replacing the old one, you can do the same with updated mods but place them in your mods. Once done all that stuff upload the updated version of the pack and change the URL of your modpack to the new URL of your updated ZIP of the pack. Make sure you apply a changelog so users can look at your changes to the modpack. Same goes to the beta platform although there is a current bug with it so when you update the new platform, a update notification doesn't come through to users via launcher4