All is possible. I am not sure, that what you want is the best way. In the most cases I recommend to use some standard way, then your live will be easier especially after change to a new version of the control which you use.

If you do want to have this you can use custom formatter (see code example in http://stackoverflow.com/questions/2991267/jqgrid-editable-column-that-always-shows-a-select/2992064#2992064). But after implementation of such feature you will see other problems and have new wishes. So I do recommend you better use some standard way already implemented in jqGrid.