DyNaer: nope you dont have to download anything at all : place the installer in the same directory name the downloader uses :
if the game's installer has changed (even with the same version number used), the downloader will redownload the whole game.
An installer could have a same version number , but the hash will be different....
HypersomniacLive: Yes, I know about this - it's still a bit inconvenient for me as I rename the game folders (the way GOG names them really sucks, imho) and move them to a different partition, yet better than having to actually re-download. Does this work with third-party downloaders other than the GOG Downloader?
What I mean by my question is how do I know when to do this check if the installer version number stays the same? I've seen some users here report that they do a weekly check but I'm too lazy to do this, plus I'd have to give up the way I organize my GOG games.
well the directories names aren't friendly for sure
check ConnieThunder's folder on Skydrive ---->
http://www.gog.com/forum/general/gog_file_sizes_and_md5s/post113 there're 2 batches files, you can edit them to fit your liking (removing the games you don't have aswell)
sure, make a backup before doing anything.
I can't seriously say when to do this , i guess it depends your maximum download speed (if you have many games to grab for the lastest updates), so could be once a week or a month.
I personaly have another method for the games which getting a v2 installer : i maintain a spreadsheet and check only the remaining games which have a v1 installer (about once week). -> way faster. But for the others ones i must count on the others / notification system . But in the case of the same number installer : it's a problem :/
I guess some people here have some skills in coding, which i don't, so i do with what i have or could do.