If there are cracks in the mortar of a masonry, it means you have movements in the house, and that's not something to be taken lightly?!
Is the house sinking in a corner, or is the frost lifting it up in the spring?
Sure, you can repair the cracks with new mortar, but they will surely reappear just like cracks in an old face that has been covered up with makeup if you don’t remove the cause first.