No, an easy option is to simply shift every timezone by an hour and keep UTC intact. A ton of places already do that twice a year for daylight savings.
I never understood why we mess with UTC so much when we already have another widely used mechanism to keep the sun and clocks aligned.
And maybe we should stop touching political timezones by then anyways.
But given the amount of time it is going to take to accumulate so much as another leap minute's worth of leap time, let alone an hour, I'm pretty confident we're in the "arrogant" branch if we start declaring what they need.
P(nobody cares about UTC anymore anyhow | someone had to solve the problem of incorporating non-terrestrial time which is way harder than leap seconds) would seem to me to approach 100%. You can decide which branch you want to take, but P(things just keep on keeping on without much change from today for the next several thousand years) seems not large enough to start trying to make lots of plans for.
Random local government people declare it is to be, and ... as an industry we largely figure it out.
The more responsible governments give amble notice and as an industry we are very very good at that (you not realizing it, is an example).
And good riddance to leap seconds! It was too hard for us to figure out, and they didn't do anything useful for anyone.
So the example given Feb-31 is stored as 1 month + 30 days past the start of the year and would trigger right on time march 2nd or 3rd, depending on leap year. In fact I started doing it to handle birthdays on leap day, there is not always a February 29, but there is always a day 29 days after the start of February.
* https://leginfo.legislature.ca.gov/faces/codes_displaySectio...
A century later we'll finally be able to fix Earth's orbit to make a nice round 360 days per year, 12 months of 30 days, nice and clean, no more complexity or confusion... ah, that'll be the day.
... of course you're talking about events that would be approximately 4000 years from now!