You might find a component in the tool palette that almost matches a component that you use in your drawings. Rather than creating a new component, you can change a single instance of a component by editing its symbolic geometry in the block editor. Only the symbol is edited. Annotations and other component data is preserved.
For example, if the P&ID tool palette contains a tank that is similar to one you want to use but is not as tall as you need it to be, you can edit the component and stretch the lines to create a new instance.