You can combine manual and autograding for a Jupyter assignment as below - 

First go to the Grading section of the part and add rubrics for manual grading -
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Follow the steps to create cells for auto-grading.  For the Jupyter Release step, please make sure to unselect  the flag "Delete unused grading items"
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Now, you can follow the manual grading process to give scores for the rubrics that are manually graded.