If five years have passed since the last accident involving a covered process, and that process meets the other two requirements identified under 40 CFR §68.10(b) for Program 1 eligibility, could that process become a Program 1 process even if it had previously been identified as a Program 2 or 3 process?

Yes. The status of a particular process can change over time. Any process that meets all of the criteria listed at 40 CFR §68.10(b) is eligible for Program 1 status, regardless of the prior status of that process. If the owner or operator chooses to change Program levels, he must file an updated RMP to reflect this change in program level within six months of becoming eligible for Program 1 (See 40 CFR §68.190(b)(7)).