it is but that is just the way it is packaged and released but the code will likely be the same of the single player package plus MP stuff and all the extra content that is MP related and we still don't know precisely.
so for instance if I am able to mod the SP client to change the damage of weapons could I do the same with the MP client and use it as exploit? Having access to SP modding surely will give access to lot of intelligence on how things works on the MP client. This is my understanding though, I might be wrong
I get what you're saying but, I highly doubt that will be an issue. Even if they do use the same code they can just do a scan for modifed data on startup.