Its easier if you work around this. The barbs wil always have the city style of the first tribe to play. So you can give this tribe the industrial or modern city style (via ascribing Ind, or E2 and Aut to them), and the barbs will keep the old citystyle. Additionally, if you make these techs no,no techs things will stay in place (unless you need other tribes to get the industrial/modern styles during the game, in which case this won't be a good idea)
If you want to work around giving city styles etc after you begun building the scenario, you can use CivTweak, a smart little util made by Carl Fritz (available in the dl's of this site)