Transforms describe a set of modifications to be performed on an existing MSI for the purpose of customizing it. This is ordinarily done by making a copy of the MSI to be customized, modifying the copy and then using the old and the new MSI to generate a transform. For example:
copy openafs.msi openafs-modified.msi
(edit the openafs-modified.msi to include the necessary changes)
msitran -g openafs.msi openafs-modified.msi openafs-transform.mst
(generates openafs-transform.mst, which is the transform)
Transforms have an extension of .mst. 'msitran' is a tool distributed as part of the "Windows Installer" SDK (part of the Windows Platform SDK).
You can test a transform by:
copy openafs.msi openafs-test.msi
msitran -a openafs-transform.mst openafs-test.msi
and then checking the resulting openafs-test.msi to see if all changes you have made above to openafs-modified.msi is present in openafs-test.msi. 'msitran' will complain if some modification in the transform can not be successfully applied.
As mentioned above, you can use a tool like ORCA.EXE to edit the MSI databases directly when editing openafs-modified.msi. More details are given below.