It is possible to escape the variable sign % by inserting a backslash before it. In this way you can use a notation similar to a variable without being expanded.
Examples
%DD%-%MM%-%YYYY% = 15-08-2018
%DD%-\%MM\%-%YYYY% = 15-%MM%-2018
%DD%-\%%MM%\%-%YYYY% = 15-%08%-2018