I don't see anywhere atm where setting the mac address exists in Studio. There are certain rules in setting the address manually that need to be followed e.g. the first three bytes be prefixed with 00:50:56 so it is important to find out the specifics for your product+version prior to making these changes.
On the other hand, if it is having them show up in your known_hosts and avoid the challenge you can workaround this with a ssh config rule.
Adding something like the following to the ~/.ssh/config might accomplish what you are looking for.
UserKnownHostsFile /dev/nullStrictHostKeyChecking noAs always, consider security implications before configuring ssh rules.