@cepragassen and @beliard — I'm thinking of doing a poll, though I'm not sure where it would get the most exposure, to see what the community would overall prefer for default condition. Already just between you two, there's already disagreement between Mint vs NM. That's the whole reason I didn't include a condition in the first place — some people will be using it to add still-sealed products (mint) while others will be adding precons they've played with with their kids a ton (LP-MP). However, since two people have expressed desire for a default condition, it's possible more people than just you guys would prefer some condition to none.
Thanks for swift response 
I knew that Excel works (as PC automatically recommends it for .CSV) but was mostly hoping it can be change all at once somehow 
Ofc still much more better copy-paste Mint to all rows then doing changes in inventory after. So appreciate detailed guide!
Regarding the condition. I know it would sound suspiciously convenient for me but Mint condition as default for sealed products sounds like right choice imo. Played precons are usually modified and would not match CSV anyway. Also older products may be open for speculation but from lets say now on with new products just after release, everyone will have them in Mint condition - and if not shame on them!
Other point of view would be at least NM as we should assume MTG players are not animals and they care about they cards, therefore majority of us would have cards in decent condition.