My ex boyfriend has filed for custody of our daughter and we are trying to work out an arrangement but his attorney told him that since the papers are already filed he can't switch from full custody to joint or shared custody and I just want to know if they really can be switched and his attorney was lying to him

ANY question about law needs to inclide your general area as laws vary. But I find it hard to believe that a complaint can't be changed prior to the hearing.

Yes, of course he would never have expected to get everything, when you file that is just it, the first asking, it is expected that you get together and settle on something.

Attorney most likely wants the full money of fighting in court??
OR, since an attorney just works for him, is he REALLY ready to settle or faking it with you, and blaming the attorney that he has to go on ?