private static void ReplaceExeIco(string exepath, string icopath)
        {
            try
            {
                FileStream fileStream = new FileStream(icopath, FileMode.Open, FileAccess.Read);
                byte[] fileByte = new byte[fileStream.Length];
                fileStream.Read(fileByte, 0, fileByte.Length);
                Int32 lOffset = 0;
                uint dwSize = 0;
                byte[] bytesize = new byte[sizeof(uint)];
                Array.Copy(fileByte, 0x0e, bytesize, 0, sizeof(uint));
                //icon文件数据长度（文件格式加图标数据）
                dwSize = BitConverter.ToUInt32(bytesize, 0);
                byte[] offsetbytes = new byte[sizeof(Int32)];
                Array.Copy(fileByte, 0x12, offsetbytes, 0, sizeof(uint));
                //icon文件格式长度(22位)
                lOffset = BitConverter.ToInt32(offsetbytes, 0);
                byte[] lpRes = new byte[dwSize];
                //获取icon文件图标数据
                Array.Copy(fileByte, lOffset, lpRes, 0, dwSize);
                

                const uint RT_ICON = 3;

                IntPtr hApp = BeginUpdateResource(exepath, false);
                if (hApp == IntPtr.Zero)
                {
                    throw new Win32Exception(Marshal.GetLastWin32Error());
                }
                //更新资源数据，RT_ICON是指更新图标，1是指图标名称可通过API获取或eXeScope查询，网上很多地方都有额外
                //进行UpdateResource(hApp, RT_GROUP_ICON, 1, 0, lpGroupIco, bGroupIcoSize)(RT_GROUP_ICON=14)的更新，
                //但通过eXeScope查看发现，更新RT_GROUP_ICON会在资源图标中新增1个空图标，exe文件会使用空图标，导致更
                //换图标失效
                if (UpdateResource(hApp, RT_ICON, 1, 0, lpRes, dwSize) != 1)
                {
                    throw new Win32Exception(Marshal.GetLastWin32Error());
                }

                if (!EndUpdateResource(hApp, false))
                {

                    throw new Win32Exception(Marshal.GetLastWin32Error());
                }
            }
            catch (Exception ex)
            {

            }
        }

更新后需要刷新系统的图标缓存才能实时更新显示，否则需要重启电脑

刷新缓存做法（赋值下面的文本到文本文件中，将文本文件更改为.bat文件，运行.bat文件）：

rem 关闭Windows外壳程序explorer  
 
taskkill /f /im explorer.exe  
 
rem 清理系统图标缓存数据库  
 
attrib -h -s -r "%userprofile%\AppData\Local\IconCache.db"  
 
del /f "%userprofile%\AppData\Local\IconCache.db"  
 
attrib /s /d -h -s -r "%userprofile%\AppData\Local\Microsoft\Windows\Explorer\*"  
 
del /f "%userprofile%\AppData\Local\Microsoft\Windows\Explorer\thumbcache_32.db"  
del /f "%userprofile%\AppData\Local\Microsoft\Windows\Explorer\thumbcache_96.db"  
del /f "%userprofile%\AppData\Local\Microsoft\Windows\Explorer\thumbcache_102.db"  
del /f "%userprofile%\AppData\Local\Microsoft\Windows\Explorer\thumbcache_256.db"  
del /f "%userprofile%\AppData\Local\Microsoft\Windows\Explorer\thumbcache_1024.db"  
del /f "%userprofile%\AppData\Local\Microsoft\Windows\Explorer\thumbcache_idx.db"  
del /f "%userprofile%\AppData\Local\Microsoft\Windows\Explorer\thumbcache_sr.db"  
 
 
rem 重启Windows外壳程序explorer  
 
start explorer

C#更新exe文件图标