Please, no! %{__cp} hugely decreases readability and if the situation happens that mkdir and cp are not in the $PATH we will have much bigger problems than running sed on all .spec files.

I am sorry but this will hit even if you don't use macro when tools are not in $PATH, unless you use full path 
 
Use just plain Unix commands as $DEITY intended them to be used.
I believe macro give you plain Unix command with full path. 



;)
V!jay