You would start at CCSE level/exam if you hit the worst case scenario.
For your ideal scenario you probably need an authoritative answer from Check Point. @Jason_Tugwell can jump in here.
I would encourage you to seek CCSME and to do a new Specialist exam.
You'd get a 2 year CCSME certification rather than a possible extension (if option 1 is possible and it works that way)
Its all about the spirit of the certification path and certification rather than the number of exams.
I recommend CTPS. It is a very interesting course and has great labs. It covers IPS, AB and AV very well and has great labs.
Another recommendation I make to CCSME and other students is to get CCSME and then as soon as possible pass as many Specialist exams as you can (or want to) as soon as you can after achieving CCSME.
Each Specialist exam you do after achieving CCSME gives you a one year extension to CCSME.
There are CCSME certified people who have the CCSME valid until 2033 and beyond. Me included.
It's easier if your job requires the courses and exams but for anyone who can and does go the distance they are rewarded with a long lasting high-level certification.
I appreciate its not for everyone but it's out there for anyone who can.
BTW. CCTA R82 is out now. The course.
No exam for it yet but the exam will follow in the next few months. Its currently under development.
Another great course. Lots more focus on packet capturing and analysis on the cli and with Wireshark. Plus troubleshooting CCSA R82 topics, including IA and APPI & URLF.