How to update with latest files, msi?

 Recently I got a requirement to update only a particular sub folder in the msi.

Instead of creating a complete new msi , we created only a config msi which will have only this sub folder.

But during installation on top of parent msi, it is not copying the latest files if the file version is same, (they should update version number, but not our team :) )

So same version but date modified different, but still ignoring to replace with new file if old file exists.

The fix for this is to add property

REINSTALLMODE = amus

Instead of regular VOMUS.