We've added Tallybot to help with your M-1 adjustments.
For Non-taxable income and Non-deductible expenses, (the most common M-1 types), simply select the M-1 tax categories and Tallybot will make a Journal Entry for you. See it in action here.
Your M-1 Report automatically updates.
Here are some close up screenshots.
For the other two M-1 types, (Not on books types), additional taxable income, and additional deductible expenses, first make a JE to get the numbers on the books and then select the M-1 tax category (on the offset account)