Thank you, Andi !!!
It seems that Bikini Girl uses a pin system somewhat similar to her sheriff cousin from the late 1970s.
However the "frame" system appears to be totally different.
It looks like a conversion would be rather simple. From what you've shown us in JOSO's picture, perhaps it would be just a matter of drilling out the factory pin and replacing it with a vinyl pin that just fits snug enough to hold everything together, but still permits repositioning of each leg.
Thanks again and all the best,
Richard
See attachments of Playmobil's 1970s sheriff with movable legs.