How can I remove glue from leather without ruining the leather?
Take a scrap piece of leather and apply several dots of glue to it, then let them dry.  Once they are dry, try each of the following solvents to see which ones remove the glue with a minimum of discoloration to the leather.  Then stain the leather to see how the solvent treated leather accepts color.


clean water, 
water with dish-soap, 
rubbing alcohol, 
acetone (nail polish remover) 
dilute ammonia 
dilute bleach


Never mix the solvents with each other.  Apply each solvent to a separate dot of dried glue using a q-tip or folded paper towel.