Page History

...

The following definitions show the different change types. 

Addition change
If an element has been addedIn the context of used project impact analysis, an addition change occurs. It is important to note that changes occurring when changing from one used project version to another (and elements from recovered elements to good ones) are considered as element additions and are treated to be the one when an element is restored from a recovered state to a normal one. Such element change is represented in the green rectangle in rectangle in the Affected elements panel panel.

Deletion change
If an element has been removed, a deletion change occurs. The deletion change usually results in composition integrity errors, i.e., it causes the appearance of recovered elements, since the deleted element is still used in the main project.

...

The Accept Changes button switches the used project version to the selected one. You will be warned if the selected version will cause or leave unresolved references. 

Reject Changes restores  restores the project to the version opened state before invoking the Impact analysis window. The analysis with all of the local changes you had as well. The same applies for X (closing the dialog).