You can find and modify the cells using cells.find(), cells.findXy() and cells.findByPixels() methods:
http://api.daypilot.org/daypilot-scheduler-cells-find/
http://api.daypilot.org/daypilot-scheduler-cells-findxy/
http://api.daypilot.org/daypilot-scheduler-cells-findbypixels/
Example:
dp.cells.find("2016-10-01", "A").html("10/1/2016");
You can also control all cells in a row:
http://api.daypilot.org/daypilot-row-cells-all/
dp.rows.find("A").cells.all().html("A");
The row headers can be accessed using rows.find():
http://api.daypilot.org/daypilot-scheduler-rows-find/
var row = dp.rows.find("A");
and modified using addClass(), removeClass(), column(i).html():
http://api.daypilot.org/daypilot-row-addclass/
http://api.daypilot.org/daypilot-row-removeclass/
http://api.daypilot.org/daypilot-row-column/
dp.rows.find("A").addClass("resource-a");
> We have disabled the progressive rendering,
Unfortunately all performance tweaks work with progressive rendering because that's the only scalable solution. The progressive rendering improves scalability at the expense of delays during scrolling. You can tweak the delays (see http://doc.daypilot.org/scheduler/scrolling-performance/) but it it can't be completely eliminated.
You can also check your implementation of real-time rendering events (like onBeforeEventRender, onBeforeCellRender). Older IE version are particularly sensitive to inefficiencies there - try to make them as fast as possible. You can check if this is the problem by turning them off temporarily.