"until EXIT or next Section comes".
Not really. EXIT does nothing.
MOVE 1 TO A-FIELD
MOVE ZERO TO A-FIELD
In changing from the use of SECTIONs just for the sake of it, you run the danger of wasting time and getting something different.
If the SECTIONs contain paragraphs, you're going to have to change to PERFORM ... THRU ... which is an ugly, inflexible, way to do it, and which is prone to several types of error.
Once a program is compiled, it is irrelevant whether there are SECTIONs or paragraphs in it. By that time it is just "object code", with Assembler versions of "go to" of various types.
The example of what you are proposing changing it to is useful to be able to highlight potential problems in making the change, which is set against none/very little benefit.