Thanks for asking.
Let's try and understand how X Theme licence works. Each licence entitles you to setup two type of environments, Production and Staging. When you are developing the website then you can validate the dev URL in Staging environment and once development is completed and ready to launch, in that case you can switch to Production. Point to note over here is that for each unique website you are developing requires you to buy a new copy of X Theme from Themeforest.
However, In your case as you are asking (and I am assuming that while using word 'integrity' you are referring to a unique copy of X Theme) that website A no longer requires X Theme and you want to use the same licence on website B? Absolutely, you have that option. All you need to do is under licence manager page change the URL that's assigned.
More information can be found on product validation documentation.