Did you add that line in the appropriate level of the government building that exists in Larissa (or alternatively in all of them)? If yes, then since the peasants are still available after that, it means that the resource is not being added to the region.

Are you sure you've not exceeded the EDU/DMB/EDB limits of units, models, resources?If you're sure, then the only thing I can imagine is wrong is you're not deleting map.rwm or your changes are not being saved. Are you running the pc as system administrator/have you disabled Vista's UAC control?