I'm sure you've noticed that when you double-click on certain objects in your drawings, certain commands start. Double-clicking on text opens the text editor, double-clicking on a block opens the the Attribute Editor or the Block Editor (if the block doesn't have attributes), etc.
But what if you don't like the default action? For example, double-clicking on a dimension launches the Properties palette by default. But I'm much more likely to be editing the dimension text than I am to be changing one of its properties. (Adding notes like TYP. or V.I.F. of course, NOT changing the default number!) So I'd rather that double-clicking on a dimension launched the text editor instead.
To change this, I'll go into the CUI, look for Double-Click Actions, right-click, and choose New.
Now, I need to add the command I want to my new action. To do this, I can search or browse the command list, then drag-and-drop the command onto the action. (Watch out -- you want "Text, Edit" or DDEDIT here. Dimension Text Edit and Mtext Edit will NOT give you the same results.)
That's it! Now, after you click OK, double-clicking a dimension will open its text for editing instead of opening the Properties palette. And of course, this method works for adding just about any action to any kind of object (although it helps your sanity if the two are related).