C# Signature:

[DllImport("advapi32.dll", CharSet=CharSet.Unicode, SetLastError=true)]
public static extern Boolean ChangeServiceConfig(IntPtr hService, UInt32 nServiceType, UInt32 nStartType, UInt32 nErrorControl, String lpBinaryPathName, String lpLoadOrderGroup, IntPtr lpdwTagId, String lpDependencies, String lpServiceStartName, String lpPassword, String lpDisplayName);

VB Signature:

Declare Function ChangeServiceConfig Lib "advapi32.dll" (TODO) As TODO

User-Defined Types:

None.

Alternative Managed API:

Do you know one? Please contribute it!

private const uint SERVICE_NO_CHANGE        = 0xffffffff; //this value is found in winsvc.h
private const uint SERVICE_QUERY_CONFIG        = 0x00000001;
private const uint SERVICE_CHANGE_CONFIG        = 0x00000002;
private const uint SERVICE_QUERY_STATUS        = 0x00000004;
private const uint SERVICE_ENUMERATE_DEPENDENTS    = 0x00000008;
private const uint SERVICE_START            = 0x00000010;
private const uint SERVICE_STOP             = 0x00000020;
private const uint SERVICE_PAUSE_CONTINUE           = 0x00000040;
private const uint SERVICE_INTERROGATE        = 0x00000080;
private const uint SERVICE_USER_DEFINED_CONTROL     = 0x00000100;
private const uint STANDARD_RIGHTS_REQUIRED         = 0x000F0000;
private const uint SERVICE_ALL_ACCESS =   (    STANDARD_RIGHTS_REQUIRED     |                                             SERVICE_QUERY_CONFIG     |
                    SERVICE_CHANGE_CONFIG    |
                    SERVICE_QUERY_STATUS     |
                    SERVICE_ENUMERATE_DEPENDENTS |
                    SERVICE_START        |
                    SERVICE_STOP         |
                    SERVICE_PAUSE_CONTINUE       |
                    SERVICE_INTERROGATE      |
                    SERVICE_USER_DEFINED_CONTROL);

Notes:

To use this function, make sure you call OpenService with the SERVICE_CHANGE_CONFIG flag. Look at OpenService and QueryServiceConfig for more examples.

Tips & Tricks:

Remember that the cofiguration settings will only be in effect the next time the service is started.

Sample Code:

IntPtr databaseHandle = OpenSCManager(null, null, SC_MANAGER_ALL_ACCESS);
if(databaseHandle == IntPtr.Zero)
    throw new System.Runtime.InteropServices.ExternalException("Open Service Manager Error");

m_pServiceHandle = OpenService(databaseHandle,  strServiceName, SERVICE_QUERY_CONFIG | SERVICE_CHANGE_CONFIG);
if(m_pServiceHandle == IntPtr.Zero)
    throw new System.Runtime.InteropServices.ExternalException("Open Service Error");

//This code is changing the password for the service.

if (!ChangeServiceConfig(m_pServiceHandle, SERVICE_NO_CHANGE, SERVICE_NO_CHANGE, SERVICE_NO_CHANGE, null, null,
    IntPtr.Zero, null, null, value, null))
{
    int nError = Marshal.GetLastWin32Error();
    Win32Exception win32Exception = new Win32Exception(nError);
    throw new System.Runtime.InteropServices.ExternalException("Could not change password : " + win32Exception.Message);
}