Then update the link to not take them to the portal, but to the survey. This will only work if they are already logged in, or if the survey is public for anyone with the link. I don't know if that's something you want on HR cases.

I am not sure what your 3 points mean, after reading the last line. It feels like something is copy/pasted here that shouldn't have? And 1 and 2 are basically the same: if you only update it for HRSD surveys (create different notifications), they will receive different emails.