A microprocessor having model specific registers (MSRs) includes, for each of the MSRs, an associated default value that indicates whether the MSR is protected or non-protected and an associated fuse that, if blown, toggles the associated default value from protected to non-protected or non-protected to protected. In one embodiment, microcode that does the following in response to the microprocessor encountering an instruction that accesses a specified MSR: determines whether the fuse associated with the specified MSR is blown or unblown, uses the default value associated with the MSR as an indicator of whether the MSR is protected if the associated fuse is unblown; toggles the associated default value to generate the indicator if the associated fuse is blown; protects access to the MSR if the indicator indicates the MSR is protected; and refrains from protecting access to the MSR if the indicator indicates the MSR is non-protected.