I think this is what you are trying to do...

This worked in my own testing, other than I occassionally had to click the buttons twice before they worked, I think it is a focus issue, but I couldn't quite nail it down.

This assumes that your table has Class Name of myTable, that one of the Single-Line fields in your table has Class Name of myTableField, and that field has the checkbox marked for "Previous data and new rows with lookup data will be read-only, but user-added rows will be editable."

Add this CSS to your form: 

/*Set the appearance of the custom Add and Delete buttons on the table*/
.myButton { 
  display: inline-flex; 
  align-items: center; 
  font-size: 14px; 
  position: relative; 
  max-height: 30px; 
  min-height: 30px;
  background-color: #007bff;
  color: white;
  border: 0px;
  border-radius: 7px;
}

Add this Javascript to your form: 

$(document).ready(function() {
  
  //When the form loads, call the RemoveDeleteFromDisabledRows and ReplaceDeleteAndAddWithButtons functions.
  $('.myTableField input').each(RemoveDeleteFromDisabledRows);
  $('.myTableField input').each(ReplaceDeleteAndAddWithButtons);
  
  //When the table changes, call the RemoveDeleteFromDisabledRows and ReplaceDeleteAndAddWithButtons functions.
  $('.myTable').change(RemoveDeleteFromDisabledRows);
  $('.myTable').change(ReplaceDeleteAndAddWithButtons);
  
  //When rows are added to the table, call the RemoveDeleteFromDisabledRows and ReplaceDeleteAndAddWithButtons functions.
  $('.cf-table-add-row').click(RemoveDeleteFromDisabledRows);
  $('.cf-table-add-row').click(ReplaceDeleteAndAddWithButtons);
  
  //When this function is called, it will cycle through each table row and if the myTableField
  //field is disabled, it will remove the option to delete that row from the table.
  function RemoveDeleteFromDisabledRows()
  {
    if($(this)[0].hasAttribute("readonly"))
    {
      $(this).closest('li').find('.form-del-field').remove();
    }
  }
  
  //When this function is called, it will cycle through each table row and replace the delete
  //x's with delete buttons, and the add link with add button.
  function ReplaceDeleteAndAddWithButtons()
  {
    $(this).closest('li').find('.form-del-field').html('<button class="myButton">Delete</button>');
    $('.cf-table-add-row').html('<button class="myButton">Add +</button>');
  }
  
});

End result looks like this:

All this is doing is replacing the links for the add and delete items in the table with custom buttons.