my $input = "(55.950254, -3.187606)";
( my $output = $input ) =~ s{([-\d.]+),  # capture the first number to $1
                             \s+         # at least one space
                             ([-\d.]+)   # capture the second to $2
                            }
                            {$2 $1}x;     # reverse $1 & $2

print $output;