Can federal sex crimes be reduced from felony by plea bargain?

Looking at Federal Charges sex crimes, I was told by the first lawyer I talked to that all crimes can be reduced to even no registration required. The second attorney said no they can't. I understand each crime has guidelines for sentencing. My question is, can the charges be reduced to a level that requires no registration as an offender? And is it likely that they might do so for a first time offender who has never been in trouble? I am trying to get it where it does not interfere with my wife's immigration to the US which might be likely to see interference now.