Yes, theoretically, any aspect of the protocol can be changed through governance, but there is a high bar for making such changes. Any proposed modifications must go through the ZIP process, which requires demonstrating consensus among various stakeholders and community members.
This is a common topic in crypto projects like Bitcoin, where some people question the integrity of the 21 million coin cap. However, significant changes to fundamental aspects of the protocol require substantial agreement within the community, including from miners, node operators, exchanges, and other stakeholders. Such a major change is unrealistic because it would undermine the foundational principle of scarcity that the community values.
With regard to the NSM, smoothing the issuance curve is necessary so that burned ZEC can be reintroduced in future block rewards in a straightforward manner. The design of the issuance curve intentionally approximates the four-year half-life reflected in current halving cycles. In ZIP 234, we state, “Future protocol changes may not increase the payout rate to a reasonable approximation beyond the four-year half-life constraint,” to demonstrate a commitment that safeguards against arbitrary changes that could alter the protocol in a meaningful way.