currently

Listbox setting for checkmarkDeselectOthers is retreived from library property only
https://www.zkoss.org/wiki/ZK_Configuration_Reference/zk.xml/The_Library_Properties/org.zkoss.zul.listbox.checkmarkDeselectOthers
https://github.com/zkoss/zk/blob/master/zul/src/org/zkoss/zul/Listbox.java#L3459
This means that the setting must be activated or disabled for all listboxes in the application.

Improvement

Use Utils testAttribute to check for custom attribute, then default to library property
https://github.com/zkoss/zk/blob/master/zul/src/org/zkoss/zul/Listbox.java#L3472
This would allow developer to override the global setting on a case-by-case need