Adding on to checkboxlist?

I have a query and it CheckBoxList1.Items.Add(reader[""].ToString().  I later on validate it so that at least one of them is check marked and at most three of them are checked.

But I've learned that I now have to pull from that query two, probably three fields.  As it is, the checkboxlist1.items are separated by spaces.  I'm going to need to separate them into a table like view... and probably save the strings somewhere because I'm going to submit the text to the database.

Can I make changes to the CheckBoxList class or is it bad practice to do so?  What's the best way to do this?