Linking one-line symbols to the main schematic symbols is done in a similar way to schematic/footprint associations. After inserting the one-line symbol, you can click "Schematic" or "Panel" to bring up a list of component tags you can link to. If you use the "Schematic" option, just be sure to select all the information you want to copy over, and ACE should do the rest. The one-line symbol will update along with the panel and child symbols when you change the schematic, or vice versa. You can surf to them as well.
Creating your own one-line symbols isn't terribly hard, but there are a few things you do differently. I'll direct you to this help page about creating one-line symbols and this help page about schematic attributes for more info on the topic.
One thing to note, and I learned this from this forum, if you do a project-wide retag and your one-line diagram sheet is positioned before the sheets that contain its parent components, ACADE will tag the one-line symbols based on their position on that page, then update the rest of the schematics/footprints accordingly. On my drawing I ended up with all the AC Drives being tagged like DR123456A, DR123456B, ... , DR123456P, DR123456Q, etc. Move your one-line drawings to the end of the drawing set before doing a project-wide retag to avoid this. It's not fun.
