The icon library that is opened is dependent upon the active project and whether there exists a customized version of the icon library in one of the active project's search paths. If there are no customized icon libraries in the search paths for the active project, then the default icon library that ships with Elevate Web Builder will be opened.
If you want to customize the icon library that ships with Elevate Web Builder for the active project, simply use the File/Save As menu option to save the default icon library interface file in a different folder/directory. You should always use the default interface file name "TIconLibrary.wbi", even for customized icon libraries. If you do not use the correct interface file name, then the customized icon library will be ignored.