With the release of Interspire Email Marketer 6.0 several years ago the functionality was added to develop and install custom addons that don’t require the editing of the core files and code. The advantages of this type of development are clear. Anytime you edit the core files of the software program you make it more difficult to add future functionality and you make it difficult to upgrade the core software program to future releases and updates.
If you edit the core code of Interspire Email Marketer it becomes very important that you keep very close track of which files and have edited and how. That type of development log will make it much easier in the future. The next time you want to add a new functionality or when you want to upgrade your installation of IEM to the latest version you will be able to more carefully look at the list of edited files and determine if there is crossover. Where there is crossover you may attempt to merge the code from the new files with your edited files to preserve your developement.
As you can see it makes far better sense to develop new functionality in Interspire Email Marketer as part of an actual addon. Addons are installed into the installation and can be enabled or disabled with a single click from the Settings>Addons screen. (See screenshot below)
If you were to upgrade core files to a new version and find there is some conflict with one of your addons you can easily disable it while you troubleshoot without having to take Interspire offline. You will never have to worry about merging code again.