swift, 115 bytes

Result

AC

Duration

1016ms

Code [DL]

var x=0
while let l=readLine(){l.map{x=$0=="T" ?0:$0=="K" ?x-49:(x+1)%50;print(x<1 ?"x":$0,terminator:"")}
print()}

stdin

                                 T                
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                                                  
                  K                               

stdout

                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                                 x                
                  xxxxxxxxxxxxxxxx                

stderr

/tmp/code.swift:2:26: warning: result of call to 'map' is unused
while let l=readLine(){l.map{x=$0=="T" ?0:$0=="K" ?x-49:(x+1)%50;print(x<1 ?"x":$0,terminator:"")}
                         ^  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

strace