I use KendoMvcGrid in my webproject, i choose the option "GridEditMode.PopUp" for add and edit features. I search to not display the modification in grid when my popup in display.
If I understand correctly, you want to have a popup to edit rows in a grid, but you don't want the changes to be shown in the grid while the popup is open. Unfortunately, the row and the edit popup are bound to the same data, so changing one will change the other.
If you really need to implement the behavior you're describing, you could use a custom command button that calls a function, which in turn opens a popup with a form that lets you edit values and save them.