The most important element of an organization's risk register to update following the commissioning of a new financial reporting system is the risk rating of affected financial processes. A risk rating is a measure of the level and nature of the risk exposure, based on the impact and likelihood of the risk events. A risk rating can help to prioritize and respond to the risks, and to monitor and report the risk status. A new financial reporting system may introduce new or different risks, or change the existing risks, that could affect the financial processes of the organization, such as data quality, accuracy, timeliness, compliance, or security. Therefore, the risk rating of affected financial processes should be updated to reflect the current risk situation and to ensure that the risk register is accurate and complete. Key risk indicators (KRIs), the owner of the financial reporting process, and the list of relevant financial controls are not as important as the risk rating of affected financial processes, as they are not directly affected by the commissioning of a new financial reporting system, and they do not measure the risk exposure and impact of the financial processes. References = CRISC Review Manual, 6th Edition, ISACA, 2015, page 48.

A gap analysis is the process of comparing the current state of the organization's compliance with the new regulation and the desired state of compliance. It helps to identify the gaps or deficiencies that need to be addressed and prioritize the actions to close them. Performing a gap analysis is the first step to understand the impact of the new regulation and plan the appropriate risk response.
References
*ISACA CRISC Review Manual, 7th Edition, Domain 2: IT Risk Assessment, Section 2.2.3: Gap Analysis
*Regulatory Change: Future of Risk in the Digital Era | Deloitte US
*Gap Analysis: What It Is and How to Perform One | The Blueprint

Risk is inefficiently controlled when the annual cost of the control exceeds the annual loss expectancy (ALE) of the risk, as this means that the organization is spending more on the control than the potential loss that the control is supposed to prevent or reduce. This indicates that the control is not cost-effective or optimal, and that the organization should consider alternative or complementary controls that can lower the cost or increase the benefit of the risk management. Control is ineffective and should be strengthened when the control does not reduce the likelihood or impact of the risk to an acceptable level, regardless of the cost. Risk is efficiently controlled when the annual cost of the control is equal to or less than the annual loss expectancy (ALE) of the risk, as this means that the organization is spending less or equal on the control than the potential loss that the control is supposed to prevent or reduce. Control is weak and should be removed when the control does not provide any benefit or value to the risk management, regardless of the cost. References = CRISC Certified in Risk and Information Systems Control - Question205; ISACA Certified in Risk and Information Systems Control (CRISC) Certification Exam Question and Answers, question 205.

The risk register element that is most likely to be updated if the attack surface or exposure of an asset is reduced is the likelihood rating, as this reflects the probability or frequency of a risk event occurring. The attack surface or exposure of an asset is the measure of the extent and accessibility of the asset to potential threats or attackers. If the attack surface or exposure of an asset is reduced, the likelihood of the asset being compromised or damaged by a risk event is also reduced. Therefore, the likelihood rating of the risk should be updated accordingly. The other options are not the risk register elements that are most likely to be updated if the attack surface or exposure of an asset is reduced, although they may be affected or influenced by it.
Control effectiveness is the measure of how well the risk controls reduce the risk level or achieve the control objectives. Assessment approach is the method or technique used to identify, analyze, and evaluate the risks.
Impact rating is the measure of the magnitude or severity of the consequences of a risk event on the asset or the organization. References = Risk and Information Systems Control Study Manual, Chapter 2: IT Risk Identification, page 54.

Identifying and assessing the risk scenarios associated with IT strategic initiatives is the best risk management approach for the strategic IT planning process, because it helps to understand and evaluate the potential or actual threats or opportunities that may affect the achievement or implementation of the IT strategic initiatives, and to determine the appropriate risk responses and controls. A risk scenario is a hypothetical situation or event that describes the source, cause, consequence, and impact of a risk. A risk scenario can be positive or negative, depending on whether it represents an opportunity or a threat. An IT strategic initiative is a project or program that supports or enables the IT strategy, which is a plan that defines how IT supports and aligns with the organization's vision, mission, and strategy. The strategic IT planning process is a process of developing, implementing, and monitoring the IT strategy and its associated IT strategic initiatives.
Identifying and assessing the risk scenarios is the best risk management approach, as it helps to anticipate and prepare for the potential or actual outcomes of the IT strategic initiatives, and to optimize the risk-reward balance and the value delivery of IT. Establishing key performance indicators (KPIs) to track IT strategic initiatives, reviewing the IT strategic plan by the chief information security officer (CISO) and enterprise risk management (ERM), and developing the IT strategic plan from the organization-wide risk management plan are all possible risk management approaches for the strategic IT planning process, but they are not the best approach, as they do not directly address the identification and assessment of the risk scenarios associated with IT strategic initiatives. References = Risk and Information Systems Control Study Manual, Chapter 2, Section 2.1.1, page 37