You won’t be able to use your PC while the icon pack is being installed since explorer and all related processes need to be closed. Just make sure you create a restore point before messing anything up. That said, I have actually installed icon packs over icon packs and haven’t run into trouble, might I add, yet. After that, reboot the system and see if things are working. It’d rather be a good practice to first uninstall any previous icon pack. I’d advise not to go an installing spree like you’re probably used to on your Android device or Linux.

Keep in mind these are still replacing system files.