G'day craigt,

"I have not been able to substitute or transform, split, or substr."

You could use any of those methods. I'm assuming by "transform" you mean transliteration (i.e. y/// aka tr///). I acknowledge that some of these solutions have already been posted.

substitution

$ perl -E 'my $x = "A(B"; $x =~ s/\(/</; say $x'
A<B
[download]

transliteration

$ perl -E 'my $x = "A(B"; $x =~ y/(/</; say $x'
A<B
[download]

split

$ perl -E 'my $x = "A(B"; $x = join "<", split /\(/, $x; say $x'
A<B
[download]

substr

$ perl -E 'my $x = "A(B"; substr $x, index($x, "("), 1, "<"; say $x'
A<B
[download]

Now use Benchmark to compare the different methods. Please post the results as I (and probably others) would be interested.