1050F won't hurt the temper on steels that are heat treated already. The only ones I know that would be affected are PH stainless that are aged at a lower temp than the salt bath and that would be rare and very hard steels. They would go down in strength if the salt bath temp is higher. 1050 is the lowest I can recall working with so the heat treater could just do a SBN at 950 for a longer time period without bothering the temper at all. Other steels are going to take quite a bit more to mess with. For instance you can do a subcritical anneal on 4140CM (lots of guns made out of 4140) at 1440F but to fully anneal you'll need 1550F.That is contrary to what I have been told by folks that do SBN
FYI I worked in machine shops for about 25 years. Aerospace, oilfield and automotive.