With the PUBG Mobile 0.12.0 update, the "portable closet" can be used during match.

Previously, it was only usable at the starting island but now it can be used outside of the starting island as well.

You cannot change your skin during combat, and you have to stand still without making any moves to change your skin.
This means, it is benificial to change your skin in a safe area.

※ There is a cool-down time of 5 minutes after changing your skin.

Hope you can change into various skins during the match which leads to victory!