Switching between cores

I have Roon on a dedicated server and on a MacBook with two separate libraries.
I only use the Laptop for travel and it has it’s own library on the hard drive. I would never use the 2 cores at the same time.How do I switch between cores and then back.

Simplest way, using a remote switch the one you want to use on leaving the other off. It will look for a core and if the one it finds is not the one the remote last saw it will let you choose it and offer you the option to de-authorise the last one. You can switch between the two as often as you like.

Are you talking mechanical switch

Simply go to Settings > General and click on Disconnect. You’ll then see a Choose Your Roon Core screen. IIRC correctly, you only need to add your credentials when first connecting to a core.

I have a similar question. I want to install Roon on a friends system and be able to use the Roon app on my iPhone to control her system when I am at her apartment, but also to control my own system when I return home. I will purchase a separate core for her system. How difficult is it to switch to a different core from the app without transferring the license?