Thank you for the reply.
I have performed these steps myself and am certain of the solution. There shouldn’t be any risk involved with the suggestion I provided in my initial reply.
In essence, to change the main login email address, we must first add the new tenant admin member and then remove the old tenant admin member.
As an extra verification step, you could try logging in with the preferred email address after being invited to ensure that it works. Only after this is complete can you proceed with removing the old tenant admin member. This way, you can have certainty that you do not lose access to your account.
Kind regards,
Rueben