Whenever you start using variables like field0, field1, etc., it should be a red flag that you should probably be using arrays. The code could be more like this:

foreach my $rowref (@rowrefs) {
  my @sassified = map { sassify($_) } @$rowref;
  print FILE join("|", @sassified),"\n";
}
[download]

You could even do that in one line if you really wanted to:

print FILE join("|", map { sassify($_) } @$_), "\n" for @rowrefs;
[download]

And in your sassify function, if you have alot of s///'s to perform on a variable, its more perlish to put it in a for loop:

for ($in) {
  s/this/that/;
  s/here/there/;
  etc.
}
[download]

Disclaimer: Code above is not tested, and I'm sorry to say that none of this will help much with the speed.