design pattern when you want to keep original data untouched and add some custom data

I have a challenge at hand to keep original data untouched let's say it's an array of users with properties. Sometimes I want to modify or add custom values for some of those properties for example change age of a user but i don't want to spoil original data and let the opportunity to remove customization altogether or by one. Is there any design pattern which I could try to use for this?