I agree with Scott. A GDL object is the same as an AutoCAD 'Block' ... with this exception: blocks are embedded within the dwg file, but the gdl object is external.
Just like a block, if you edit a GDL object's content, all placed elements are updated.
If you do not have the shortcut key cmd-shift-O (ctrl-shift-O) set to open a GDL object, you might want to assign it or something similar. You then just select the placed object, issue cmd-shift-O and edit away. If your 'block' content is just 2D content, then you edit visually in the 2D symbol window.
Related to your question: if you have symbols/etc from autocad days that are stored as 'blocks' in existing dwg files, AC makes it easy to convert those blocks into GDL objects via both a File menu option as well as dwg translator options.
Cheers,
Karl
AC 28 USA and earlier • macOS Sequoia 15.3, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators