For example, to add breaklines just inside the left and right sides of the pattern, use
Or, try this:
Special Note: Each breakline must consist of either all odd numbers, or all even numbers.
If all this is too confusing to deal with, take a look at Constructing a Celtic Knot by Marc Wallace. The "Inside Borders" he describes are what I call Breaklines.
His example is a 3x3 knot with breaklines as follows:
1,3, 1,5, 3,5
He has 4x4 and 5x5 examples with the breaklines shown on a grid. You'll have to figure out the coordinates to get them to work here.