Being forced to serve notice period

I am currently employed in an organisation where my signed appointment letter specifies a notice period of 60 days. During my tenure, the company later introduced a revised notice period of 90 days; however, I did not sign or formally acknowledge any document agreeing to this change, and it was not communicated to me in writing at the time of my joining. While my appointment letter includes a clause stating that employees must abide by service rules that may be amended from time to time, the notice period is already explicitly mentioned in the appointment letter. I now intend to resign and am willing to serve the 60-day notice period as per my signed contract, while also respectfully requesting consideration for an early release depending on project requirements. In this context, I would like legal clarity on whether the company can enforce the revised 90-day notice period despite the absence of my written consent, whether such a change can be applied through internal service rules without employee acknowledgment, and what legal options or precautions I should consider to ensure that my resignation and exit remain compliant with my contractual obligations while allowing for a smooth and professional transition.