You can modify the cells on the fly using the cells API, e.g.
dp.rows.find("A").cells.all().html("A");
You can also add/remove CSS classes using .addClass() and removeClass().
See also:
https://api.daypilot.org/daypilot-row-cells-all/
It's not really tested to be compatible with an ongoing time range selection but it looks like it could work.