After his initial plan was rejected by letter, did Damu Anna take any further action to get Baba's permission?

Yes, despite his profound disappointment, Damu Anna did take further action. As narrated in Chapter 25, the reply letter he received also contained a hint, likely from Madhavrao, suggesting a personal visit. The message was, "There is a difference between hearing and seeing; you should come here in person." Clinging to this shred of hope, Damu Anna decided it was right to go to Shirdi, thinking that perhaps Baba would give him permission if he asked face-to-face. He traveled to Shirdi, sat near Baba, and began massaging his feet, but ultimately found he lacked the courage to bring up the subject again.