A request XML packet that changes site settings should include the set operation node:
<packet version="1.6.3.0">
<site>
<set>
...
</set>
</site>
</packet>
The set node does not have a separate type, it is nested within the complex type (site.xsd). The set node has the following graphics representation:

It indicates sites to be updated with the specified information. Data type: siteFilterType (site.xsd). To see the structure of this node, proceed to section Available Filters.
It contains a collection of settings that will be set for the filtered sites. Data type: none.
It specifies a collection of general site settings that will be set for the filtered sites. Data type: setSiteGenSetupType (site.xsd). To see the structure of this node, proceed to section Node set/gen_setup.
It specifies a collection of preferences for the filtered sites. Data type: domainPrefs (plesk_domain.xsd). To see the structure of this node, proceed to section Site Preferences.
It specifies hosting settings for the filtered sites. Data type: siteHostingAgentSet (site.xsd). To see the structure of this node, proceed to section Hosting.
It specifies the amount of disk space allotted for email boxes and mailing lists on the filtered sites. Data type: none. To see the structure of this node, proceed to section Disk Space Usage.