That is true.Any Day with this much recoding should be replayed.... and Capt, you forget that you actually changed some of the relp awarded in choices in Day1 (Cassie's swimsuit opinion choice for example).... the outcome of the current Day1 can be different from the outcome of the previous Day1. Just making it clear for folks to understand and keep expectations in check.
However, as the same variables are defined, it will not impact your end-game save.
Obviously if your "old save" is on day one, or two.... you'd better play the rework of day one.