It would be great to be able to use mail merge fields (customer ID for example) in URLS in notification emails.
As of today (unless I miss something), it's not possible to use these mail merge fields when inserting an hyperlink. It is possible to write an URL that ends with a Custom field and the email client will treat it as an URL, but it would be great to use such fields when inserting hyperlinks.
Here's how you can link merge vars with text.
Let us know if you have any questions.