Yes it is.
That's cool that you have such problems - we can see it and can improve the grid.
There are some ways to solve this problem.
The best way - allow user to specify style settings declaratively, for example:
columns.Add(o => o.Customers.IsVip).AddCssClass("myclass");
I think made a default cell renderer as internal was a mistake and we need to open his. After that you can make an extension method to do this, or specify it obviously:
var column = columns.Add(o => o.Customers.CompanyName)
Also I think we need specify a public setter for CellRenderer property, if you want to replace the default behavior (rendering "<td>" element).
I made a some fixes for this problem, you can see it in the repository, if it's ok I will update the grid in the near future.
You can modify "_Grid.cshtml" or create a new one, and use it to render custom columns, like this:
@foreach (IGridColumn column in Model.Columns)
if(column.Name == "CustomColumn")
Not so good, but...