Ok, first you've got to create a CommandButton to execute the VBA-Code.
Unfortunately I only know the german version of MS Excel so you'll have to search for it on your own. It's probably a window called "tools".
After adding the Commandbutton open the VBA Editor, pressing ALT+F11
Now paste the following code
this code checks if Cell A1 has a value >= 12
in case it's true, it transfers the value of cell D1 to C1 and all values according to the font property such as font-family and size and color a.s.o.
if A1 is <12 or empty it does nothing
Good luck searching the tools-window 
Simon
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