c:\@Work\Perl\monks>perl -wMstrict -le
"my @lines = (
   'some text foo | some text BAR | oh , no , commas | some text BAZ | some text QUX',
   'some text Oof | some, text, BAR | some , text , BAZ | some text QUX',
   'some, text, FOO | some text BAR |  one two | some , text , QUX',
   );
 ;;
 my $got_commas = qr{
   (?: (?<= [|]) | \A) [^|,]* (?: , [^|,]*)+ (?= [|] | \z)
   }xms;
 ;;
 for my $line (@lines) {
   while ($line =~ m{ ($got_commas) }xmsg) {
     my $before = substr $line, 0, $-[1];
     my $after  = substr $line, $+[1];
     print qq{:$before$_$after:} for split m{ , }xms, $1;
     }
   }
"
:some text foo | some text BAR | oh | some text BAZ | some text QUX:
:some text foo | some text BAR | no | some text BAZ | some text QUX:
:some text foo | some text BAR | commas | some text BAZ | some text QUX:
:some text Oof | some| some , text , BAZ | some text QUX:
:some text Oof | text| some , text , BAZ | some text QUX:
:some text Oof | BAR | some , text , BAZ | some text QUX:
:some text Oof | some, text, BAR | some | some text QUX:
:some text Oof | some, text, BAR | text | some text QUX:
:some text Oof | some, text, BAR | BAZ | some text QUX:
:some| some text BAR |  one two | some , text , QUX:
: text| some text BAR |  one two | some , text , QUX:
: FOO | some text BAR |  one two | some , text , QUX:
:some, text, FOO | some text BAR |  one two | some :
:some, text, FOO | some text BAR |  one two | text :
:some, text, FOO | some text BAR |  one two | QUX: