Loading pharmacy data from Ravimiamet/State Agency of Medicines and merging it with current OSM data is now complete.
For future reference/maintenance - here are source fields and OSM tags that were mapped 1 to 1:
Site name - official_name or name (depends if the pharmacy is a branch/haruapteek or not)
Site reference number - ref
E-mail - email
Activity licence holder - operator
Tags like phone/geographic coordinates/addr:* might have some differeces in OSM data and source.
I ended up writing my own tool that transformed changes from csv to osm xml. Main advantage was that I could work safely with limited subset of tags. More about it here.