WSProxy-update-regular-de-to-sendable.html

<script runat="server">  
Platform.Load("core","1.1.5");  
try{
var prox = new Script.Util.WSProxy(); 

var CustomerKey = "xxxxx-xxxx-xxxx-xxxx", //Insert DE External Key
    IsSendable = "true",
    SendableDataExtensionField = {"Name": "email", "DataType": "EmailAddress"}, //Provide the name of the field used to establish a data relationship (SendableDataExtensionField relates to subscribers on SendableSubscriberField)
    SendableSubscriberField = {"Name": "Subscriber Key"}; //Use "Subscriber Key" or "Email Address" depending on whether the SUBSCRIBER_KEY business rule has been turned on.

var res = prox.updateItem("DataExtension", {"CustomerKey":CustomerKey, "IsSendable":IsSendable, "SendableDataExtensionField":SendableDataExtensionField, "SendableSubscriberField":SendableSubscriberField});
Write(Stringify(res));  

}catch(e){
Write(Stringify(e));
}
</script>