Rewriting or patching?

It's a question that almost any programmer has to face sooner or later.

Deciding which side to stand is really depending on many issues, one of which should be preserving valuable content from the old software.

This matter has been discussed several times in the Monastery, and without repeating what was said, I offer you the links, so you can judge by yourself.

• Value of "RE"-coding for the newbie
• (OT) Rewriting, from scratch, a huge code base
• Rewriting a large code base

I liked very much two articles that were referred in the previous links, where a practical approach to rewriting was described in great detail. It's not an easy task, but it makes sense the way it is described.

• An article by Joel Spolsky about rewriting badly written but functional software
• Another Joel's article about reading code

There is no better teacher than experience, so I would recommend to try your skills at a module of your project, so that you can appreciate the magnitude of the task. While you are at it, take into account everything dws and adrianh has said about isolating the changes and testing them.

Good luck!