hmm...
I'm not clear on if the email address is one per account or one per certificate.
In other words, when you update the email address for certificate X, that may change the email address for that entire account.
Reading through the link @MikeMcQ posted, it seems to be account based [not per certificate].
Although, you could use separate accounts on each of your systems and thus be able to receive individual emails per system.
But LE won't send many per one expiry email.
For that you must use a group/distribution list.