I would like to raise the soil level around my 8 month old Japanese maple. I need to raise it by about 4 inches. will this cause the tree any shock or worse, death?
For outdoor living trees raising the soil level 4 inches over the entire root area which extends out to the edge of the drip line will usually kill a plant. See this answer and this answer for more explanation. Trees exchange air through their roots and they cannot do so if the soil is suddenly raised.
For indoor or potted plants you will be better off to remove from the pot and add the soil at the bottom of the pot.