I would like to change the email registered to receive expiration notices for my domains.
It seems the let’s encrypt simple windows client does not support changing the email address registered initially. There´s a new parameter for email but reading the documentation it seems to be intended for use with offline installation.
Tried running the command with said parameter anyway but I can´t seem to find a way to see what my registration information server side is currently.
I have access to a linux box and tried setting up Certbot, hoping to use it´s update registration command. I however can´t seem to find out how to link the bot with my current registration.
That's unfortunate! Have you thought about opening a feature request with the client developers? I can definitely see other users wanting to do this in the future.
You'll have to find a way to get Certbot to use your account private key from the Windows client in order to do this. I'm not sure how to help achieve that, it's likely to be pretty tricky and require some deep understanding of both ACME clients.
In the short term my suggestion is that you create a new account using your Windows ACME client and set the contact address correctly at the time of creation to the new address you want to use. Migrating to a new account will require re-authorizing your domains and issuing new certificates which is a bit of a pain but probably less of a pain than hacking around with private keys between different ACME clients.