Most everything your asking involves code modification. You can ask such questions over at http://www.photopostdev.com
as we here support the normal code.
I can tell ya database fields are never hidden but you can hide a variable in a forum using an input tag much like we pass other hidden variables. You can search many templates to see an input tag and how it looks hidden.
Code can not be stored in the database and if you modify the files to allow html then all users will have this ability normally