According to the DH Hydromatic manual, and this one is dated 1969, there is no upper limit for the angle of bend which can be straightened, only how bent it can be against sectional area, before it has to be annealed prior to straightening.
It also states that any blade can be straightened twice but must be annealed prior to straightening a third time. (probably easier to find a better pilot at this stage!!)
If there is a bend in the first 8.2″ from the shank end on a Merlin blade it cannot be reworked.

In reality I know that they are often scrapped when bent nowadays.

Pete