To determine the extent to which Italgas S.p.A. should utilize hybrid bonds, we first evaluate the company's financial position at the end of 2022 (as of 2023-01-01).

1.  **Calculate Total Adjusted Capital (TAC):**
    *   Total Liabilities (2023-01-01): 8,639,987,000 EUR
    *   Total Equity (2023-01-01): 2,390,570,000 EUR
    *   TAC = Liabilities + Equity = 11,030,557,000 EUR.

2.  **Determine S&P Global Ratings' Cap:**
    *   The cap on equity credit for hybrid instruments is 15% of TAC.
    *   Cap = 0.15 * 11,030,557,000 = 1,654,583,550 EUR.

3.  **Evaluate Financial Capacity and Debt Structure:**
    *   Italgas has substantial long-term financial liabilities (6,402,913,000 EUR) and a high level of capital investment (Intangible Assets and Goodwill at 8,509,368,000 EUR).
    *   With an operating profit of 641,338,000 EUR and stable core revenue, the company has the capacity to service debt. However, market conditions shifted significantly in 2022, with swap rates (5Y, 7Y, 10Y) rising from near-zero/negative in 2020-2021 to ~1.7%-1.9% in 2022. This environment increases the cost of traditional debt financing.
    *   Given the high level of existing debt and rising interest rates, utilizing hybrid bonds can help manage the credit profile by securing equity-like capital treatment for up to 15% of TAC without diluting existing shareholders as much as straight equity. 
    *   Considering the goal of maintaining financial flexibility while optimizing capital structure, utilizing a significant portion of the available hybrid capacity is financially prudent. Among the provided options, 100% represents the full strategic utilization of the regulatory allowance, which is consistent with active capital management for a capital-intensive utility company facing higher borrowing costs.

<answer>100%</answer>