Hello Willem!
Thanks for posting your question regarding using the same BoldGrid theme on two different websites. Your BoldGrid Premium Connect Key is used to enable the BoldGrid plugin features. It does not save your theme to use on two separate websites. With that said, you would need to enter the Connect Key for each website as outlined in our guide: Activating Your BoldGrid Connect Key. Once you have entered this into both websites, you will need to use select the Inspiration for each instance and begin building the website(s) on each instance of BoldGrid. The changes you make on one site will not affect the other(s) with the same Connect Key.