Dynamic load of Game Objects

In case of “skin” I mean that level have some standart parts: background, wall, road, paralax layer and etc.(Some of them are sprites, some spine objects, but all level skins have same parts). For example first level “snow pack”, second “city pack”, third “space station” and etc. When I load level data (Json with information about level), I need to select what skin to use (for example if in level data skin value is “1” I need to load collection “1” (“snowPack”)), and generate level by it parts.
About car. In start of the race I need to create car with character that use one of car, and one of character. I need to create 8 cars with character, but every user have different cars with different characters and I can’t create it staticly.
I only wont to know mechanis how to load only 8 of them without loading all.