How do I modify pin assignments to use my signal names in Quartus Prime?
The issue you are having is not the way you are assigning pins, that is being done correctly. The problem is in the file that is being used as the top level entity. The pin assignments apply only to the top level entity, and only code in that entity will be compiled.

According to the error messages, you have currently got a module called DE1_SOC_golden_top set as the top level entity which is declared in a file called de1_soc_golden_top.v. This file is not actually added to the list of project files (hence the warning), but will still be in the project directory so it is using that one. If the file didn't exist on the disk any more you would have got an error instead saying the module could not be found.

Your schematic is however called light.bdf which means you need to set the top level module to be light which is done by right clicking on the schematic file in the project list and selecting the "Set as Top Level Entity" option. Once you recompile the new top level module will be used.