The placement of 3d modelled buildings within a district appears to be essentially hard-coded within the district "grid". So when you copy a building from one type of district to another, the building is placed in the same relative position within the district. But Firaxis does not seem to place Building_Level_1 for a district always at location XY within all districts. So the library may be placed at XY in a Campus, but a Shrine may be placed at YZ, and a Lighthouse may be placed as position AB. This is all I learned from watching Sukritact model and place his custom building for Mali's Unique District. Beyond this I know nothing.
In order to copy the 3d art of an existing building and then re-position the model within the district I think you would actually have to copy the definition file for the existing Firaxis-made building, and then edit its placement position within a district directly as part of the new artdefinition you have created by copy-pasting the original definition.