I am about to change a part of my application over to CoreData. I have a custom class that I wrote that I want to convert to NSManagedObject. Before I go through all of this I would like to make sure that it will work. Do I just need to make an entity in the CoreData file and change the subclass? are there any other considerations?
The documentation is very useful on this point. In particular, you want to read the part of that document named 'Subclassing Notes'.
Things to consider would include: are you using any objects that are not supported by Core Data? If so, you'll want to either make them non-persistant, or if that isn't an option you'll want to look at implementing non-standard persistent attributes
The documentation I've linked to above should be pretty helpful: it's pretty clear and straightforward. To be honest it is difficult to tell how much of an effort it will be on your part: if your NSObject subclass is relatively simple it could be a very straightforward process. But if you're working with something more complex you will want to consider the points raised in the docs above.