Dropdown in ALV with description only and fcode triggering

Hello,

may be this kind of question have many times duscussed before, but i didn't find any of them as answered,

May requirement is something 2 fold.

I have a Editable alv with dropdowns using class cl_gui_alv_grid, below screenshot.

What i want:

1. I need the description to appear strictly without key, in place of key.

For example:

01 should be replaced by primary school

02 should be replaced by lower secandary and so on.

When ever user select any description, its key should gets captured in internal table.

It seems that this can be achieved using conversion exits, but i don't have enough info how to use them exactly.

2. Whenever any value is selected from dropdown, Function code should gets triggered(like in module pool)

and based on that values choosed, i want to change/refresh grid.

Please guide me .