Altering the sleeves of a garment of any kind will change it. People will sometimes want to update the sleeves because the fashion trends have changed.
People sometimes don’t notice how fashion trends can affect the way that the sleeves on a dress or a shirt can look. However, sleeve types can change with the times, just like everything else. More rounded sleeves have been popular at certain points in time. At other times, it was more common to see sleeves that were shaped to the arms and shoulders more strongly.
People will always need both short and long sleeves, of course, so it’s rare to see time periods where sleeves of particular lengths have completely fallen out of style. However, the shapes of those sleeves might change nearly as often, which will still have a subtle effect on the way that an outfit looks to lots of people.
Making slight alterations to almost any dress or other garment can already make it seem like it was from a different time period, since the majority of fashion trends are very subtle. When people are able to add new sleeves to their dresses to make them look different, they’ll hold onto the rest of the garment for a longer period of time.