Question about saving the version of FO4 pre-Anniversary update to an external HD

I have put off updating my FO4 to the anniversary edition because I’ve seen all the game breaking bugs and was worried about the save file breaking bugs. I have hundreds of hours and am level 130 on one of my playthroughs and I’m not about to jeopardize losing it all. I ordered a 2 TB Seagate external HD and today it came in the mail. I want to save my current version of FO4 to it and I’ve just never done this before. So will it save my game as is, and if something wrong happens when I update to anniversary edition, theoretically will I be able to plug in the hard drive with the pre-anniversary save version on it? And everything run like it is right now? I have most of the creation club stuff that comes with the new bundle and I’m wondering if I’ll still be able to access that as well if something goes wrong and I have to play the game off the external HD with the pre-anniversary version. I’m a newbie at using external hard drives so this is just an overall question on how to do this properly and if my theory will actually work. Thanks for anyone that answers with help or confirmation!

Bethesda bugs.. Bethesda bugs never changes..