Once I have installed the boost upgrade kit, do I need the tool or is it the hub that you can change without the tool?

Once the hub is installed, you can comfortably swap between pulleys using an Allen key to remove the 5 screws holding the pulley to the hub. You don't use the pulley removal installation tool again for the process of swapping between pulleys. To give you a better idea as to the process, please refer to the fitting instructions in the link below:

http://www.maceengineering.com.au/WebRoot/ecshared01/Shops/mace/4E1D/A79D/D800/6FA9/364C/C0A8/D240/1463/PULLEY_INSTALL_instructions_pdf.pdf