Allow me to clarify the answer behind the answer.
Do you as a GM want your player to split his previous experience and future improvement rolls between two separate skills? If yes, then tell your players that different sizes of hammers require different specialised combat techniques.
If on the other hand you'd like them to spread their points a little more diversely, then tell them that as part of being a civilised blacksmith he also is forced to participate in the militia, so both types of weapons are learned as a single style.
What you choose has long term ramifications to character roundedness, development and advancement speed.
That was the gaming answer. For the historical combat answer, what I will say is that historically, combat was taught as a collection of different weapon styles. You didn't learn a single one in isolation, but as part of a combination to teach you adaptability in both using and facing different cultural weapons.
Is 1-h-hammer the same as 2-h-hammer? Technically there are obvious mechanical differences, yet both styles share common ground in reading your opponent, ranging, knowing the best places to strike, etc. In real life a good fighter should be able to carry over most of his ability to any weapon he picks up.
How you ultimately want to model this is up to you, but we've written RQII to be flexible in this regard. :wink: