Sometimes, while customizing screens in the configuration workbench, you might run in to the fact that even though you can see a field in a context node in the workbench, it may not appear in the available fields in the configuration workbench...
In many cases, this is due to the design layer hiding the field because SAP has decided this is a technical field, and not relevant for end-users. If you want to decide otherwise, you can easily copy the design layer object, and in your copy, change the setting for your field from 'hidden' to 'standard'.
Copying and changing design layer objects is done in the IMG.
SAP Customizing Implementation Guide -> Customer Relationship Management -> UI Framework -> UI Framework Definition -> Design Layer ->Copy SAP Design Objects
In this IMG transaction, you are able to select the right design object and make a custom copy of it. Note that when opening the transaction, this may take a while due to the large amount of data in the maintenance view. Don't worry, eventually, the data will show up. It may take more than a minute.
Before you can start, you need to know which design object to copy. You can determine this by clicking F2 in the webclient, and note the object stated under 'Design Layer'.
In the design layer customizing, find the right Object Type, and click 'Design Object' on the left to see the details.
Now select the right design object, and either click on Design on the left of the screen to see the details of the standard Design Object, or click on Go To Copies if a copy has already been made, or click 'Copy from SAP' if you want to adjust the field properties.
In the details of the design object, you can influence whether the field is 'hidden' or 'standard'. Hidden fields are not available in the UI Configuration tool.
There are some more options available in the Design Layer Customizing, such as changing the field label and implementing a value help.
Note that changes you make here will be automatically applied to all items in the webclient that use this design object.
If you want to know where a design object is used (in order to know what the impact of your change will be, go to the design object details page (by double-clicking on the 'Design Object' node on the left of the screen), and click the 'Where Used' button.
The result will be an overview of the components/views where the design object is used. This thus is a list of impacted views if you make a change here.