local $_;

# Read entire file into $_.
{ local $/; $_ = <IN_FILE>; }

# Execute substitutions once each.
s/^[ ]+//mg;
s/[ ]+$//mg;
s/
   :000[AP]M
   |
   99991231
   |
   Jan\ 1\ 1900\ 12:00:00
//xg;
s/[ ]*~\t~[ ]*/~/g;

# Output entire file.
print;