If I start a project off using Blueprints can I change some of the code in C++ as I go?
There’s no inherent limitations either way - if you start with a blueprint project you can move some of it to C++ or vice versa. In fact, if you watch some of Hourences tutorials he talks about setting up some of his game systems in blueprints and later replacing them with C++. You can even use C++ to create your own custom blueprint nodes if you like.
While you cannot edit the code for the Blueprints themselves, you can easily add code classes to any project by selecting File -> Add Code to Project. This will give you a class creation “wizard” that will provide you with a .h and .cpp file with basic formatting to work with Unreal Engine 4. As Hyperloop mentioned, you are not limited to using just one or the other. Most projects will mix both C++ and Blueprints to some extent.
Thank you for your help