Your 4-line breakdown looks correct to me, assuming you are recording this on a payment form, which is always tax-inclusive. (A purchase invoice for a restaurant would be fairly unusual.)
But as I said before, this seems like an horrendous amount of work. This is especially true when you consider it would need to be done, not just for client dinners, but for every meal while on business travel, etc.
I would consider a scheme with only the full-rate tax code. First, I would set up three expense accounts:
- Tax-inclusive meals
- Non-taxable meals
- 50% Meals
The only purpose for the first two is to simplify splitting at the end of the accounting period. Otherwise, they could be a single account.
I would enter a meal on 2 lines, distinguishing only the portion that was taxable from the portion that was not by initially posting those two lines to Tax-inclusive meals and Non-taxable meals. Then I would make one journal entry at the end of each tax filing period to move half of both those accounts (for the accounting period) to 50% Meals. Here is an example for a 100 taxable meal, 10% GST tax rate, and 15% non-taxable gratuity.
The payment is entered, including the tax in the amount on the Tax-inclusive meals line. No tax code is selected. (Leading numbers in Account
fields in this example are account codes used to group accounts together for display.)
On the balance sheet, Tax payable has not changed, because no ITC tax amount has so far been entered. The transaction is, to this point, being treated as though the tax were non-offsetting:

and the expenses show up on the P&L:

At the end of the accounting period, this journal entry is made. Note that the full-rate tax code is applied only to the debit to 50% Meals from the Tax-inclusive meals account:
Now the balance sheet shows a debit balance in Tax payable, representing the ITC on 50% of the taxable meal charge. (If there were normal tax collections from customers in this account, the balance would probably be in credit.)

The P&L shows the adjusted expense accounts:

In this example, 55.00 plus 7.50 represent your total, non-deductible meals expenses, including taxes that could not be used as ITC’s. 57.50 is the amount spent that can be deducted. Of course, the missing 5.00 from the restaurant bill of 125.00 went to the Tax payable account as an ITC.
The critical step with this approach is that the only place the tax code is applied is to one debit line in the journal entry at the end of the accounting period. And the only other extra step is the need to split the restaurant payment into two lines, but you would have to do that with the approach you were trying to get to anyway. And that’s a lot better than splitting every meals payment into four lines.