To achieve the desired behavior you described, you could use the Reference Attribute tool in Revit. This tool allows you to add reference information to your text, and it will automatically update if the referenced element changes.
Here's how you can use the Reference Attribute tool:
In the Project Browser, go to the section (Section A) where you want to add the reference text.
In the Annotation tab, go to the Text panel, and click on the Reference Attribute tool.
In the Reference Attribute dialog box, select the type of reference you want to add, such as a section reference.
Select the section (Section B) you want to reference from the dropdown list.
You can also specify the format for the reference text, such as adding the section number and page number, in the Format field.
Click OK to insert the reference text into your section.
To add a leader, you can use the leader tool in the Text panel to draw a line from the reference text to the location of the referenced element.