If a new editor makes changes holus-bolus to the upcoming school yearbook, they do a complete overhaul, changing everything at once. They replace all the student volunteers, arrange for a complete redesign, and find a new printer.
Holus-bolus came into use in the mid-1800s, and there are at least two stories about its origin. The English word bolus means "ball," or any soft, round lump of something, and it could be that holus was attached to suggest "whole" while imitating the look and sound of Latin in a nifty rhyming compound. Or it could be from Greek holos bolos, already a nifty rhyming compound meaning "whole lump," followed by a change to Latin endings: Latin uses -us where Greek has -os.