Defparam
Used to change the value of a lower-level component parameter(s)
module full_adder(fco, fsum, cin, a, b);
defparam u1.and_delay = 4, u1.xor_delay = 6;
defparam u2.and_delay = 3, u2.xor_delay = 5;
half_adder u1(c1, s1, a, b);
half_adder u2(.a(s1), .b(cin),