Add CustomAction to a MSI package

We used CustomActions to implement easy and quick (possibly dirty) changes before finishing the software installation.

Start editing the MSI file (e.g. using Orca)

http://support.microsoft.com/kb/255905/en-us

It's best practice to not directly edit an MSI, but using a transform (MST) instead.

Open the table CustomAction
Add a new row, defining the following values:

Action:  <unique name>
Type:     3110

Type 38     = VBScript text stored in this sequence table.
Type 3072 = Queues for execution at scheduled point within script. Executes with no user impersonation. Runs in system context.
3072 + 38 = 3110
http://msdn.microsoft.com/en-us/library/aa372048(VS.85).aspx

Source: <empty>
Target:   <write a VBScript>

Example 1: Copying a file

Set FL = CreateObject("Scripting.FileSystemObject"):FL.CopyFile "\\server\share$\file.dat", "C:\Program Files\ExistingFolder\file.dat", TRUE

Example 2: Change registry settings

Set S = CreateObject("WScript.Shell"):X="HKLM\Software\JavaSoft\Java Update\Policy\":Y="REG_DWORD":S.RegWrite x&"EnableJavaUpdate",0,Y:S.RegWrite x&"EnableAutoUpdateCheck",0,Y:S.RegWrite x&"NotifyDownload",0,Y:S.RegWrite x&"NotifyInstall",0,Y:S.RegWrite x&"Frequency",0,Y:S.RegWrite x&"UpdateSchedule",0,Y

Change to the table InstallExecuteSequence
Add a new row, using the following values:

Action:          <same name as used in CustomAction>
Condition:    NOT Installed
Sequence:   <number before InstallFinalize>

To figure out a working sequence number, sort the rows by sequence.
Search for the "InstallFinalize" sequence number and notice this value.
Decrement the noticed value by 1 and check if this value is already used.
If not, you've found your sequence number.
If yes, renumber the values, until you got a free sequence number right before "InstallFinalize".