use constant SEARCH => 0;
use constant REPLACE => 1;

my %translate = (
  funca => [ qr/funca\( ([^,]+) , ([^,]+) ,([^,]+) ,([^)]+) \)/x,
             '"func($1,$2,XXX,YYY,$4)"' ],
  funcb => [ qr/funcb\( ([^,]+) , ([^,]+) ,([^,]+) ,([^)]+) \)/x,
             '"func($1,$2,,,$4)"' ],
);

while (<DATA>) {
    for my $key (keys %translate) {
        if (/$key/) {
            s/$translate{$key}->[SEARCH]/$translate{$key}->[REPLACE]/ee;
            print;
        }
    }
}

__DATA__
funca(10,20,30,40)
funcb(10,20,30,40)