I've steeked (cut open the knitted tube) both front and back for the blanket.  Here are some pictures of the steeking process.

First I stitched all the yarn strands down using my sewing machine.  I attempted to put that line of stitching between the lines of colour and the middle brown section.  I needed stitching on both sides of where I would cut.  Then I gritted my teeth and made the first cut, hoping I'd caught all the strands so nothing would unravel:

Halfway done cutting.  You can see both sides of the knitted fabric:



The steek is completely cut:



The front of the future blanket:



And the back of the blanket:



Now I need to block (soak, squeeze out excess water and pin into approximate shape & size I want) the front and back of the blanket, and then I'll be ready to pick up stitches for knitting the border.