How do I install a previous pack without messing up my current install?

Hi! I looked through several threads, and most of what was asked was how to install new stuff or go forward. I installed the latest update and am really happy with my game at 1.42.30.1020! Thank you! Unfortunately I could not until today set my email to my current one, so I missed the release of First Pets. Not a HUGE deal; I can live without it, BUT if there is a way to install and NOT mess up my current game, I'd love to hear how to do it. Would I have to download the install that featured the release, install that, and then overwrite IT with my current configuration? That seems like the only way, but I'd hate to mess things up. (What "My First Pet Stuff" says now when I click on it is "See Requirements" in red, and then "Download to use" in blue. I don't use Origin or the Internet/Gallery, so obviously I am not doing that. Thanks in advance!

When you have updated to 1.42.30.1020, you can install any pack afterwards, but not the G4TW packs.
You can download First Pet from this topic: https://games4theworld.forumotion.com/t33100-the-sims-4-alternative-installers-install-dlcs-in-any-order-you-want

Or

Install the G4TW version for My First Pet and again do the update 1.42.30.1020 after that.

I had looked at that topic initially and thought that that MIGHT be the answer, but wasn't sure, as most replies seemed to address the situation of not having important installs earlier on, and that is not my situation. Thanks! Downloading now!

Wanted to add that it WORKED! Thank you SO much!