Is it possible to move all figure captions from above to below in MS Word?

You could do this with a wildcard find and replace, with 2 parts (in the replace you then swap the order of the parts). In the example below, I've assumed that your caption starts with "Figure ..." and ends with a paragraph (^13), so the first part captures all text from the start of Figure to the end of that paragraph. I then assume that your picture is on the immediately following paragraph. The second part (*^13) is everything from after the end of the Figure paragraph (ie start of your second paragraph) to the next paragraph mark. \1 is the first part of the find (Figure*^13) where asterisk is all characters, and \2 is the second part of the find (the paragraph with the image). In the replace, you see it says \2\1 which means replace with the second part followed by the first part (ie swapping the order of your caption and image).