a home owners association, is a condo association...it just means there is no proffessional management company involved. (the homeowners run and manage the property themselves.) You cant disolve the association, but if you and the other unit owner agree, you can revise the docs. It is always common property on the exterior, because of the towns requirements though, not because of the builders. The town has minimum square footage requirements to build, and it sounds like this space was not large enough for 2 seperate dwellings (on 2 seperate lots). Within the docs and the deed, you could "assign" usage or designate areas, but to be sure you should consult with an attorney.
The reason we would consider attempting this is because we're buying a great property that, down the line, we'd like to be able to sell as a semi-detached single family home, instead of a condo.