my @fields = $q->param;
for my $name ( @fields ){
    my @vals = $q->param($name);
    for my $value( @vals ){
        # apply regexes here
        $value =~ s/...
        $value =~ s/...
        $value =~ s/...
    }
    if (@vals > 1){
        $q->param(name => $name, values => [ @vals ]);
    }else{
        $q->param(name => $name, value => $vals[0] );
    }
}