Hello! I am new to mapping and I am learning Hammer at the moment. Hammer is rather time consuming, so I resort to editing my peti maps with Hammer. However, I would like to change the soundtrack in my maps. But, whenever I add an ambient generic the same default PETI music plays. Any way I could do this?

The music entity is located in instances/p2editor/global_ents.vmf, named @music. But you don't want to edit that directly, since that'd break any further maps you compile in the editor. So add a logic_auto in your map, and have it Kill that music on spawn so it doesn't play. You can then add your own.