I am working on a "spaghetti-code" project, and while I am fixing bugs and implementing new features, I also do some refactoring in order to make the code unit-testable.

The code is often so tightly coupled or complicated that fixing a small bug would result in a lot of classes being rewritten. So I decided to draw a line somewhere in the code where I stop refactoring. To make this clear, I drop some comments in the code explaining the situation, like:

class RefactoredClass {
    private SingletonClass xyz;

    // I know SingletonClass is a Singleton, so I would not need to pass it here.
    // However, I would like to get rid of it in the future, so it is passed as a
    // parameter here to make this change easier later.
    public RefactoredClass(SingletonClass xyz) {
        this.xyz = xyz;
    }
}

Or, another piece of cake:

// This might be a good candidate to be refactored. The structure is like:
// Version String
//    |
//    +--> ...
//    |
//    +--> ...
//          |
//    ... and so on ...    
//
Map map = new HashMap<String, Map<String, Map<String, List<String>>>>();

Is this a good idea? What should I keep in mind when doing so?