Prior to this, once gamers had chosen a skin at the start of a match, they were pretty much locked to that skin until the match has ended. However according to Blizzard, they have made some changes to the game where gamers can now still have the option of changing their skins at the start of the match.
https://twitter.com/PlayOverwatch/status/961426939067097088
This was a feature that players had requested a while back, but Overwatch’s Jeff Kaplan had stated back then that this is something that they would look at later on as it understandably wasn’t really a priority (versus balancing the game, fixing bugs, adding new features, weeding out toxic players, etc.).
That being said, Overwatch’s “Year of the Dog” event has recently kicked off where it will introduce a new capture-the-flag specific map along with a bunch of new Lunar New Year themed skins for various characters.