That will reformat the HD, and if you have a Slim, require you to have a working PUP to finish the setup so I would avoid that. Who did the last update on your PS3? I am not aware of a spoof to 3.56 for 3.41 unless they used the MFW tool to create it. I would recommend that you try to use the MFW tool to create a CFW based on 3.41 that spoofs it's version as 3.56. That should install fine.