Changing searchFields in seacrhGrid - jqGrid

I'm using jqGrid 4.3.1, and i have the following grid and seachGrid.

I need to change the values of the searchField in the searchGrid, however i cant change the grid.
I know that the search grid uses the colModels to build the searchField options, but there is anyway that i could set this values my self?

You can try to do the next if you can change table properties but not the names of the columns in the colModel.

Edit the search options of the table (Info here) and add the property beforeShowSearch wich is a function triggered before showing the form to the user. And inside this function use this selector $("#fbox_grps td.columns select") for the specified select in the image and works with it like you do with any select.