>I have a custom base class form that I use for all the forms in my app. Several custom properties exist in the base class, and then I may add a few more properties in each instance of the form when I use it.
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>What will happen if I go back and add those other properties to my base class, but yet it will already exist in certain forms that I have already made based on that class and then added the new properties to them?

I think it's going to work fine. The new properties will not be in bold anymore.