TL; DR -- Batch file to add artwork, VMCs, CFGs, VCDs. Batch file at the bottom; extract to your hdl_hdd folder inside your OPL Manager folder. Connect your PS2 HDD to your PC and install the games you want using HDLBATCH (link at bottom). Then run OPL Manager with admin rights, and set OPL Manager to scan PS2 HDD for the games list. Batch download the art files and adjust them to your liking using OPL Manager. Then run OPLBATCH.BAT by right-clicking on it and choosing Run as...
OPL BATCH - finalizing the installation of a PS2 HDD
OPL BATCH - finalizing the installation of a PS2 HDD