Thank you for your suggestion! Sorry I am relatively new at this, please correct me if I understand it wrongly.
For the WGS part, most of the links in the post are not working anymore but I managed to find the new Readme file for wgs database (https://ftp.ncbi.nlm.nih.gov/blast/WGS_TOOLS/README_BLASTWGS.txt). If I understand the instruction correctly, it only creates an alias file based on taxonomy ID provided, not downloading the sequences from database. I am hoping to download the sequences from WGS database, integrate it with nt database and build a index for taxonomy assignment on my local machine (Tools:Centrifuge, not blast). But I will give it a try if it works.