When you transform a 37xx to 34xx you need to install:
-- "34xx specific" ASR files (*.srd) via Webupdater (once)
-- "34xx specific" TTS Voices via Webupdater (once)
-- "map specific" ASR files (*.asr and *.srx) via Garminmapupdater (everytime the map is updated)
-- choose (enable in nuvi) the right TTS Voice for the right map

There is no need to rename anything, Garmin program do the right thing for you and download the right files, because they "see" your "tranformed 37xx" as 3490