If there is a situation in which you have created an MSI with Merge Modules and you don't want to recompile it because of its size or re-entry of errors, but you also want to update a merge module, then this tip will help you.
First, make a backup of the MSI.
You have to edit the MSI through ORCA. Search for the files/registry/components added by that merge module and delete them. This isn't a big task, but a simple Find option will be useful to do this.
One important thing: You need to write down the numbers of the file sequence for every file you have deleted.
Next, go to Tools - > Merge Module, Browse for the Merge Module and add it to the package.
Go to the file section and change back the sequence of files as you had copied before.
Save the package and you have completed updating the Merge Module.