In order to have the HARP software support a new product for ingestion requires quite some steps. Having a codadef to allow recognizing the right products is just one small part of this. The majority of effort is in creating the converter module in C that translates the data from the original product format into the HARP conventions.
I would not recommend trying to implement such an importer yourself. If you want to create your own importer it will be much easier to do this using a Python script as also explained in this topic.
If the type of product that you want to have supported is a public and well defined data format, you can also let us know which product this is. We occasionally add support for new product types ourselves in the HARP software based on demand.