I believe if you know the id of the control which is crmGrid_findHintText in this case will work with Javascript or JQuery
JQuery
$('#crmGrid_findHintText').val('what ever text you like') will do the work if you include jquery
Javascript
document.getElementByName('
crmGrid_findHintText'
).Value=
'what ever text you like';
Make sure to "Vote as Helpful" and "Mark As Answer",if you get answer of your question.