Edit an INI file before running the MSI

[niveknonrev]

I am very new to installshield so hopefully I am just overlooking something here.

I currently have a simple batch/cmd script that does the following:
takes 3 parameters on the command line
Uses those 3 parameters to create/edit an INI File
That INI file is then placed in the same directory as the MSI

then when the MSI is run it reads the INI file and runs silently etc.
everything works great.

The MSI is not mine it is a vendors.
I want to either transform or wrap this MSI with one of my own that can take on these 3 parameters and create/edit the INI file.

Assuming that is possible with InstallShiled - where do I even start?
How can I manipulate the INI file before executing the original MSI?

[niveknonrev]

So I figured out it doesn't seem possible to edit an INI before hand so here is what I came up with - and it got me closer but not there yet

My MSI now has the source files added so they get "installed" as in copied to the destination system.

then I use the INI File Changes section to create/edit the INI file and put it into the proper directory with the "files" the msi copied to the system.

Next I created a custom action to run the MSI that is included in my install.

BUT!?!?!?
I want the custom action to run AFTER all the files are copied to the destination system, but it is running BEFORE instead even though it is the highest sequence number and the last action to be executed.

How do I get it to run as the very last thing AFTER all the files are copied to the destination system???