Well if you know all the grammar structures and kanji as well as having a wide vocabulary you won't have any trouble with the reading and listening sections which is important. So memorising them is helpful but with languages you will also need to practise listening to and reading passages so you can recognise this grammar in a wide range of situations, not just isolated examples. Also don't forget that the Japanese exam tests speaking and writing as well and for that you need to actively practise using these structures so that you can easily use them at will.
So to answer your question, if you memorise everything in the syllabus combined with lots of practice I do believe you can ace the exam.