Hi Anshul,
1) You can make use of jQuery.ajax() function to call your transaction from your irpt or html or js. Just pass the following runner URL to the jQuery's ajax function:
This will return the result of your transaction as xml, Parse through this xml and get your desired value as string.
2) To replace the cell value, make use of the javascript functions on the grid object as,
yourAppletName.getGridObject().setCellValue(int Row, int Column, String Value)
Similarly, to pass your cell value to the transaction as its input parameter while making the ajax call, make use of getCellValue(int Row, int Column)
Hope this will solve your doubt.
Regards,
Rutika Bodas