There is a guide posted for
upgrading the internal uSD card of the Glo, in fact I used that one to upgrade my AuraHDs. It did require opening the case. There was another post that let you use all of the 4GB card, that was formatted as a 2GB card, on some Kobo devices. That was without opening the case, if I recall correctly. You can find them
here, I think.
I read a lot of epic fantasy so the world dictionary works fine for me, it is ~35MB but there are smaller ones like the "Merrian Webster 10th dictionary" at ~2.6MB. From
Github you get
here I have both working in Koreader, not sure if there is any priority to the dictionary used for the definitions returned. The dictionary file used appears in the definition message box.
Luck;
Ken