Hi, just try this,

$string='ATOM   3316  N   TYR D  24      97.479  18.805   2.990  1.00 
+36.32      D    N 
ATOM   3322  CD1 TYR D  24      96.225  15.974   2.812  1.00 17.96    
+  D    C';

$string=~s#((\w+)   \d{4}  \w   TYR )D#$1X#gsi;

print $string;

output:
*******
ATOM   3316  N   TYR X  24      97.479  18.805   2.990  1.00 36.32    
+  D    N
ATOM   3322  CD1 TYR D  24      96.225  15.974   2.812  1.00 17.96    
+  D    C

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In reply to Re: Replacing characters in a line by perlsen
in thread Replacing characters in a line by Becky

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