There was discussion about this before: have you been thinking about the ability to direct part(s) of the collection towards different paths, in case one's current partition isn't big enough for all the games?
I recall you implied you'd first make support for a separate config file (which makes sense) before adding it, so if it seems it'll take some time before this can be implemented, I might make a fork of your current work to add some quick and dirty way to channel part of my collection to a different path (like, titles starting with A => Q would be using path A, and everything else would use path B).
I would probably keep it as my personal fork as I would probably do it in some very quick and dirty way, just hardcoding something to the script, so I wouldn't feel comfortable contributing it to your work. But if you are already working on it (and have time to do it), I might just as well wait for the official implementation.
It is just that I think I think my GOG game collection (English Windows versions) has probably already surpassed the size of 2TB, which is the size of my current external USB HDD where I specifically keep my GOG installers. Hence, currently I can't really use gogrepo anymore to update or receive games. :)
So my options currently are:
1. Invest on a bigger hard drive (Nierle.de seems to be selling a 4TB 2.5" USB-powered HDD for less than 200€, that's not too bad, but still I'd need it only due to gogrepo...).
2. Make that change to gogrepo, and just extend my GOG game collection to another 2TB USB drive I have lying around unused. This would be my preferred choice at the moment.
So just if you don't think this request will materialize soon on the official gogrepo, I guess I could make that personal project fork. That would be a good way for me to revitalize my lowly python skills...