Yes, in Feb it was 4.7 to one dollar, when I left in April it was 5.7 to one dollar...
Dont change at banks, you only get 2.6.
Make friends with somebody and as +discreetly+ where you can change dollars or euros....
In Kassala there was a shop in the souk who did it quickly and for a good rate.
In Suakin people ask you if you park near the shops in the newer part of town, I didn't ask their rates.
In Dongola, people will do it in the souk also... ask carefully when you get chatting to somebody helpful....
In Khartoum, many people will do so at varying rates. Private message me and I will tell you where I did it with no problems and a good rate.
If you get caught by the police they will take all of your cash on you, maybe even more punishment.... be careful!!!
But there were a few open places that would do it, obviously paying off the police etc.
Sudan is quite expensive, so if you don;t change on the black market then it is going to be very expensive! Jowasat registration is now about 200 Sudanese pounds - thats $74 at the official rate - less than half if you use the bm.