Hi there everyone if ever i post a question as a repost i apologize. I already searched about my problem/question but i can't find any answers so my question is what as my title says.

I really want to place a 'house & lot' (example. at Twikii Island) wherein there's a beach but whenever i checked the lot where i placed it on the seaside, it goes the same as a base game lot and there's no beach that my sim can swim on.
So, any way to solve it without having the trouble of building your own beach house on the special lot?

Thanks for taking ur time to read. :/

As far as I know, beach lots must be originally built on beach lots. You could take a look at Mootilda's LotAdjustor to see if it has the ability to change that, but iirc it doesn't.

No. We still don't understand enough about the internals of beach lots to know how to change a normal lot into a proper beach lot.

However, you could extend your lot into the water using the LotAdjuster, then add buyable beach portals which you can download here:
http://www.modthesims.info/download.php?t=251392

There may also be mods which allow you to create a sand area for sand castles and sunbathing, etc. You could ask in the WCIF forum about mods which allow specific beach lot functionality.