im wondering if fin keelers are designed to be beached/careened?
The answer to that one is, no.

its not a worry grounding a long keel on sand, I'm wondering if the same carefree attitude can be taken if you intentionally or otherwise ground a fin keeper?

Fin Keeler?

Again the answer is no.
BUT. If you need to careen to work on the prop or do a hull clean, that fact that it is a fin keeler shouldn't stop you.
You need to pick your spot (not always that easy).
A creek with a sloping sandy bank is best.
Fore and aft anchors to hold the boat parallel with the shore and as close as possible.
As the tide retreats and the boat settles. from the shore pull on one of the halyards to ensure that she lays against the bank.
The weight should come down on the keel and the turn of the bilge just like on a full keeled boat.

If you are scrubbing you will need to careen twice to get to both sides.
A bit unnerving at first but at the right spot (like bums bay in the Broardwater) quite easy and safe.

We did it every 6 months when cruising SE Asia to save on slipping fees.
It was a full keeled boat though.

PS and if you do it, make sure your fuel tank is half empty, otherwise it will overflow and fill your bilge with diesel

gary

For sure careening would not be a structural design load case of most modern fin keelers. As per Gary depending on the yacht design type and build quality and upkeep it could be done at the right location with careful handling. What sort of fin keeler is it? The normal worst case keel to hull joint design case loadings are for the yacht blown over 90 degrees, or a sandbar keel tip grounding event at a reasonable speed. Neither of these involve the hull topsides being on land. Obviously many yacht designs can accommodate such a careening load case. Some Hood 23s used to - maybe still do - careen a bit off vertical against sea walls for their yearly birthday - the loads on the topsides are well less than careening on the beach at near 90degrees. Be aware that there have been instances of raft ups of modern light weight grp single skin or grp foam sandwich wide beam yachts in the middle of the raft up, with heavier boats outside them both sides of the raft up, wherein the wind and wave motions have caused the whole lot to compress against each other and the middle yacht in the string has been topside crushed. Nothing against the design of the middle yacht. Poor planning for sure but something to keep in mind.