elixir, 168 bytes

Result

AC

Duration

2287ms

Code [DL]

i=IO.read :all
x="T"
{t,_}=:binary.match i,x
{k,_}=:binary.match i,"K"
IO.puts for c<-0..byte_size(i)-1,do: (k<=c&&c<(k-(rem k,51)+t)||(rem c,51)==t)&&x||String.at(i,c)

stdin

                                                 T
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
  K                                               

stdout

                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
                                                 T
  TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT

stderr

strace