Here the source files exist in the Share Point and they are referred to using a relative file paths.
This means that you can edit the WSI file and recompile without having to install the application.

Let’s says you need to add a file called NewFile.EXE into the package for AppName-v123 so that it ends up as C:\Program Files\AppName\NewFile.EXE. To do this:
-Copy the file to
WiseSharePoint\Projects\AppName-v123\Program Files\AppName\NewFile.EXE
in the Share Point. (You might have to create folders if they don’t already exists)
Open the WSI file
In the Installation Expert view:
In Feature Details section select Files
-Add those files by browsing to them in the Share Point, NOT on the C: drive
-Click the Add File button
Wise Package Studio will add the file to the proper folder in the package.
-Save WSI package
-Click Compile to create new MSI package

(NOTE: this will overwrite the previous WSI and MSI files unless you made copies)