Using negative lookahead for the 00000000 case tightens it up: 
perl -lne 'print if s/(?<=^.{188})(?!0{8})(\d{8})(?=.{16})/20020101/' 
+original.txt > new.txt

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In reply to Re: Re: search and replace on a line by line basis by Roy Johnson
in thread search and replace on a line by line basis by Anonymous Monk

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