This is probably possible on 8.x, no need to worry about earlier versions.
Here is a really simple python snippet that will copy an existing assembly assembly into a given project, using this as a guide to http://confluence.jetbrains.com/display/TCD8/REST+API#RESTAPI-BuildConfigurationAndTemplateSettings.
import requests
xml = """<newBuildTypeDescription name='NewBuildConfigName'
sourceBuildTypeLocator='ExistingBuildConfigNameThatYouWantToCopy'
copyAllAssociatedSettings='true' shareVCSRoots='false'/>
"""
headers = {'Content-Type': 'application/xml'}
print requests.post('http://YOURTEAMCITYWEBADDRESS:YOURTEAMCITYPORT/httpAuth/app/rest/projects/id:PROJECTIDWHERENEWBUILDCONFIGSHOULDBECREATED/buildTypes', data=xml, headers=headers, auth=('TeamCityUserName','TeamCityPassword')).text