It should work just fine, but you might get the property definitions doubled in your database. The error is probably because the instances of the properties in the database that are used on pages are pointing to the wrong assembly.
Go to edit property types in admin mode to correct this. You will find duplicates of your properties, with different assemblies. The one pointing to your new assembly is probably unused, so remove it. Then change the one pointing ot your old assembly to point to the new assembly.
Just a bit of advice or opinion required really. I am considering moving EPiServer custom properties into a class library that is then referenced by the EPiServer project. The reason for this is to tidy up the EPiServer project and reduce the number of classes in the project as well as grouping them in the class library.
Has anyone done this before or had any problems doing this? I have tried and am getting errors that types cannot be loaded. Is what I am suggesting even possible or am I wasting my time trying to implement this?
Thanks in advance,