elixir, 166 bytes

Result

AC

Duration

2822ms

Code [DL]

i=IO.read :all
{t,_}=:binary.match i,"T"
{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)&&"T"||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  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
                                               T  
TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT  

stderr

strace