Run the pivot math before you decide anything else, because it usually decides for you. A beach property grossing $62k on 210 nightly bookings is running maybe $295 a night. The same unit on 30-plus-day furnished stays in a seasonal beach town might get $3,200 a month for four or five months and much less the rest of the year, so call it $28k to $34k gross. At 18% that's $5k to $6k per property against your current $11k, and mid-term work justifies a lower fee than 18% because there's no nightly turnover. Realistically you're looking at 10 to 12% on a smaller number, so those four go from $45k to something like $14k combined. That's roughly the same as the capped-nightly scenario, which means the pivot isn't a rescue. It's a way to keep the owners while the market resets.
The number that actually determines your outcome is the ops person. $52k across 12 listings is $4,333 per listing per year, and it's a fixed cost that doesn't shrink when four listings lose two thirds of their revenue. Whether you can absorb that depends on how fast you can add listings in your home city, and the honest constraint there is sales capacity, not ops capacity. If you're not already generating owner leads at two or three a month in your home market, redeploying capacity means paying someone to be underutilized for a while.
On grandfathering: existing-registration carve-outs are common in draft short-term rental ordinances and often get narrowed or dropped between draft and adoption, and the rules differ by city and state. A land use attorney in that jurisdiction is the person who can read the draft against local practice, and that's worth the hour before you write anything to your owners.
The risk you haven't raised is your owners' balance sheets. Four out-of-town owners who bought underwriting 210 nights at $295 may not be able to hold at $28k gross. If two of them sell, you lose the listings regardless of what the ordinance does, and a buyer of a capped beach property is usually a second-home user who doesn't rent at all. Ask each owner now what their debt service is. That answer tells you how much of the beach four you're actually fighting for.