You can use the updateSite endpoint to modify settings on an existing site. For example:

PUT /ccadmin/v1/sites/100002  HTTP/1.1
Authorization: Bearer <access_token>
x-ccasset-language: en

{
  "properties":
  {
    "productionURL": "www.example7.com",
    "defaultLocaleId": "3"
   }
}

The response is similar to the following:

{
  "longDescription": null,
  "priceListGroupList": [
    {
      "deleted": false,
      "repositoryId": "defaultPriceGroup",
      "active": true,
      "id": "defaultPriceGroup"
    }
  ],
  "productionURL": "www.example7.com",
  "recommendationsHost": "pt-recs-app1.us.oracle.com",
  "allowedOriginMethods": {},
  "description": null,
  "secondaryCurrency": null,
  "defaultPriceListGroup": {
    "deleted": false,
    "repositoryId": "defaultPriceGroup",
    "active": true,
    "id": "defaultPriceGroup"
  },
  "defaultCatalog": {
    "repositoryId": "cloudCatalog"
  },
  "defaultBillingCountryId": null,
  "defaultShippingCountryId": null,
  "enabled": false,
  "siteTypes": [
    "commerce"
  ],
  "recommendationsPort": "8080",
  "timeToLive": null,
  "defaultLocaleId": "3",
  "repositoryId": "100002",
  "name": "100002",
  "additionalProductionURLs": [],
  "links": [
    {
      "rel": "self",
      "href": "http://myserver.example.com:7002/ccadmin/v1/sites/100002"
    }
  ],
  "id": "100002",
  "defaultSite": false,
  "additionalLocaleIds": []
}