Markojp not anymore :) This what I do nowadays requires no knowledge about ski preparation... except maybe getting skis sharp so you don't slide down the injected courses completely out of control :D
Crgildart I admit I have never in my life put non-scraped skis on snow, but thing is still different, then with scratches. Believe me, I have done pair or two of skis in my life and I know what snow makes to wax. If nothing else, nowadays my xc skis are few years old (pretty weird, but nowadays I easier get new alpine race skis every year for "rent", then xc skis), and with current conditions we have here (basically no snow at all) you get completely new "structure" grinded in base every time you go skiing, so I see exactly this thing pretty much every day for 3-4 weeks now already :) After waxing skis look pretty cool, but after few km on snow, you see every single scratch there is on base of ski. That's why I wrote this is perfect solution when selling skis (yeah I, and I guess pretty much every other ski tech/racer, did this too when selling old skis), but unfortunately it doesn't work as "fixing"skis when you really go skiing.
But anyway, that's not really point. Point is, that for normal skiing it's completely useless to worry about little scratch like this. As someone already wrote, when you will need to worry about scratch like this, it will be your serviceman who will be dealing with it, so no need to know what to do with it :D But if it really bothers OP, then ptex "candle" (no idea how those ptex sticks which you burn and melt on base are really called in English) is way to solve this, and with a bit of luck, it will even stay there for a while. :)