You can achieve this, however this will be done at the attribute level of the entity. You will need to create a non-persistent entity lets say ValuesEntity and have its attributes same as that of your main entity of the datagrid.
Now, you can have a dataview with the ValuesEntity on your page. One you enter the values in this dataview (Single record), after this user can press a button to copy these values for all the rows of the manin entity and this can easily be done through a micorflow with ChangeObject in a loop or in a single step through OQL statement
Hope this helps