Is it possible to impersonate the System/Integration User when calling from an external application to Dynamics CRM On-Premise ?

Hello Everyone, 

I read a wonderful article on the built in System and Integration Users in the link provided below: 

http://gonzaloruizcrm.blogspot.com/2014/04/explaining-built-in-system-and.html

• I'm able to establish a connection from the external application to CRM using the Admin account. Also, when I try to impersonate any user account and perform an update operation it works.

• But when I pass the built-in System/Integration User account under CallerId, it doesn't seem to impersonate! (The update to contact record happens with the Admin User account whose credentials were used under Network Credentials)

• I'm using the below code:

NetworkCredential networkCredential = new NetworkCredential(GetValue("username"), GetValue("password"), GetValue("domain"));

CrmServiceClient crmServiceClient = new CrmServiceClient(networkCredential,GetValue("hostname"), GetValue("portnumber"), GetValue("orgname"),false,Convert.ToBoolean(GetValue("usessl")));

if (crmServiceClient.IsReady)
{
crmServiceClient.CallerId = new Guid("b8618bf1-c246-e811-9c20-00155d00ab0c");   //Impersonate UserID

Entity entity = new Entity("contact");
entity.Id = new Guid("553DAA07-4F80-E811-9C20-00155D00AB0C");
entity.Attributes["description"] = "Aloha";

crmServiceClient.Update(entity);
}

Am I missing something here? If someone has tried to use the System/Integration account to impersonate the SDK calls from external application to Dynamics CRM On-Premise, please guide. 

Thanks much in advance!