I don't think you're going to get in trouble for not claiming an expense deduction you are eligible for, but I'm not sure getting to put more in a 401k is worth it. The advantage of putting money in a 401k is that you get a tax deduction and don't pay tax on that money now, but you do pay tax on that money when it comes out of the 401k. If you properly claim an expense deduction, you won't pay tax on that amount now or ever. Also, you will have to pay self employment tax on income that would allow you to contribute to a 401k, but you will not pay it on business expense deductions, so that's another 15.3% you won't have to pay.
I suppose you could make the argument that by putting the money in the 401k you'll avoid tax on dividends and capital gains, but I suspect tax efficient investing in a taxable brokerage account would come out ahead of paying self employment and income taxes at your marginal rate on income you would otherwise not have to pay taxes on at all because it could be claimed as an eligible business expense.