А вопрос про AT LINE-SELECTION никто не отменял

To return from a high list level to the next-lower level, the user can choose Back from a detail list. The system releases the last list to have been displayed, and returns to the previous list level. The system deletes the contents of the released list.

To determine the list level in which the output from an event block will be displayed, you can change the value of the system fields sy-lsind. This is one of the few exceptions to the rule that states that you must never overwrite ABAP system fields. The system accepts only index values which correspond to existing list levels. It then deletes all existing list levels whose index is greater or equal to the index you specify. For example, if you set sy-lsind to 0, the system deletes all secondary lists and overwrites the basic list with the current secondary list.

When you change sy-lsind, the change only takes effect at the end of the corresponding event. If you work with statements in the processing block that access the list with the index sy-lsind using the INDEXaddition (for example, SCROLL), you should set the new value of sy-lsind after these statements. The best place to set it is in the last statement of the event block.

По-видимому, WRITE ... AS LINE можно использовать только непосредственно для вывода на экран.
Грустно...

Еще так же сработал старый вариант, но с добавлением сразу после modify строки
sy-uline = '-------------------------------------------------------'.