Has anyone serialized an object, written it to a text file on an SD card, and read the object back on Arduinos or can this be done?
can this be done?
It can. It's not trivial. You will sacrifice some level of accuracy if you convert any floats or doubles to strings. So, don't. The tradeoff is that the representation in the file becomes a lot more complicated.
What are you trying to serialize? I have my doubts that that is the right approach.
Doing this in a general way would take a lot of work. There is a JSON library which looks as it might provide the serialisation/deserialisation capability for you, but I've never tried it.
If you only actually need to serialise specific objects then the problem becomes rather easier, especially if you design the classes so that they are easy to serialise and deserialise. Whatever approach you take, I recommend that you do your best to separate out the abstract concepts of the things being serialised (messages, configurations, whatever) from the application logic which uses those messages/configurations.
Remember that making it work is only part of the problem - once you are using serialisation it's more or less inevitable that you will encounter versioning issues which will bring a whole new level of hassle.