Try assigning a RespositoryItemTextEdit control that cell within the GridView's CustomRowCellEdit event. Set the ReadOnly property of this RepositoryItemTextEdit to True and assign it to the cell based on your conditions.
private void gridView1_CustomRowCellEdit(object sender, DevExpress.XtraGrid.Views.Grid.CustomRowCellEditEventArgs e)
{
if (e.Column == gridView1.Columns["EmployeeName"] && e.RowHandle == 2)
{
//Don't allow users to edit Employee Name in the third row cell
RepositoryItemTextEdit readOnlyTextEdit = new RepositoryItemTextEdit();
readOnlyTextEdit.ReadOnly = true;
e.RepositoryItem = readOnlyTextEdit;
}
}