It would be helpful to be able to add a factor to multiple historic dates all at once.

For example, there’s a specific food item that I’ve consumed every day in relatively the same volume, so I never bothered tracking it. I’m now considering reducing/eliminating that from my diet, but of course I’m missing all the historical data to see how my change will impact things. It would be helpful for people who are doing elimination diets, or have changes in their environment, etc.