I was unaware you had edited your original post to provide your response, instead of saying it in a new post.
There are several qualitative differences between addition and multiplication of positive integers (at least in the English sense of "qualitative"); for instance:
there is no additive identity, but there is a multiplicative identity.
Using addition, the positive integers can be generated by a single element: 1. (in layman's terms, every positive integer can be written using as a formula involving only "1" and "+")
Using multiplication, the positive integers cannot be generated by any finite set of generators; any set of generators must contain every prime number.
1
There is an isomorphism between the positive integers under addition and a subset of the positive integers under multiplication. (Lots, actualy) However, the reverse is false.
(by Qualitative difference I mean that Quantity remains unchanged
during addition or multiplication operations between n positive integers).
I'm just not really sure what you mean by this, though...
what quantity remains unchanged? Why did you capitalize "Quantity" and "Qualitative"? By an "addition operation between n positive integers", do you mean something like a_1+a_2+\ldots +a_n where each a_i is a positive integer?
1: (A technical note: due to the way "generate" is defined,
any set of generators will generate "1"; even the empty set)