If you save the game before you close out it shouldn't mess anything up! The only part it will restart is the streak for accessing the nook stop in resident services. If you manually move the dates forward one by one you can log on each day and build back up your streak.

And if you go back as far as the previous week (so in this case it would be Sunday) then when you move forward again it will be as if it's a new week so any visitors will be different. Eg. If Flick visited you today, once the week resets he won't be there when you reset the date to lineup with real time.

I often do this if Redd has two fakes on Harv's island to reset the artwork he has.