public interface ISendLogic<T> where T : NarcoticsResult
{
    ChangeType Change_New();
    ChangeType Change_Cancel();

    PurchaseType Purchase_New();
    PurchaseType Purchase_Cancel();
}

public class SendLogic<T> : ISendLogic<T> where T : NarcoticsResult
{
    private eReportType _type;

    private bool Send_Change()
    {
        // Send to server by xml file
    }

    private bool Send_Purchase()
    {
        // Send to server by xml file
    }

    public ChangeType Change_New()
    {
        _type = change_new;
        Send_Change();
    }

    public ChangeType Change_Cancel()
    {
        _type = change_cancel;
        Send_Change();
    }

    public PurchaseType Purchase_New()
    {
        _type = purchase_new;
        Send_Purchase();
    }

    public PurchaseType Purchase_Cancel()
    {
        _type = purchase_cancel;
        Send_Purchase();
    }
}

// this class can only be used when someone wants to use change function
var logic = SendLogic<ChangeType >();
logic.Change_New();
logic.Change_Cancel();

var logic = SendLogic<ChangeType>();
logic.Change_New(); // OK
logic.Purchase_New(); // You should make this class like SendLogic<PurchaseType>()