Once you introduce your little guy to the world of breeding, you will most likely deal with secondary sexual characteristics for some time and maybe even forever..... Chances are, he will begin to mark furninture and things he deems necessary, he may have an increase in "humping" things which may include people
, I've never had a male become more aggressive due to breeding, but there are certainly some behavioral changes.... Just a bit of my 2 cents, even though you didn't ask, so I apologize in advance: Both you and your friend would be better served by finding a really reputable breeder or a hobbist involved in showing in your area and have both of your dogs evaluated. This person could also be a huge help if you do decide to breed... Its always nice to have some backup!