Would a malignant dark freckle continue to show signs of change?

Based on your description, this is most likely fine.  You can certainly have a ermatologist look at the area to confirm.  The "shadow" is to be expected, so that is not a concern in and of itself.  If the mole grows back, or more importantly gets larger, then you should have it tested.

A dark freckle could be an early Melanoma.  I would recommend that you see a dermatologist and completely remove the lesion.  If the lesion was raised enought to shave it off, it is not a feckle, so get it checked!

If you are concerned, THE HAVE THE REMAINING MOLE SURGICALY REMOVED AND EXAMINED.............................

A dark brown (not black) mole that is so small (1mm) and is not changing is very unlikely to be a skin cancer or at significant risk to become one. Please use the ABCDE's as your guide for when to be concerned about moles: Asymmetry; Irregular Borders; black or uneven Colors; Diameter greater than a pencil eraser; and a growth that is Evolving or changing. If you are still concerned, it is an extremely simple five minute procedure for a Dermatologist to remove the mole using a "punch biopsy" which typically leaves a minimal scar. The mole can then be checked microscopically for reassurance.