Can records in an individual price list be filtered by the price list tree? No.
An alternative would be filtering by price level or product group:
xxxx/cenikova-skupina/4/individualni-cenik/(cenHlad == 10)
xxxx/cenikova-skupina/4/individualni-cenik/(skupZboz == 13)
Is it possible to specify the level of detail within the object collection for price levels in an individual price list?
E.g.: /cenikova-skupina/4/individualni-cenik.xml?detail=custom:cenHlad(id,kod)
No, the individual price list does not carry information about the ID in the price level agenda (it only carries the code).