The board typically comes with U-boot and Linux pre-programmed. If you do not want to erase your flash completely, but only Linux part, than you can use U-boot to reflash.
Reflashing U-boot by U-boot is also possible, but this is not safe, as you can easily brick your board if something will be wrong in U-boot image
If the board is bricked, than yes - you have to have debug probe to program flash by flash programmer. Unfortunately, we offer only one debug probe at that time.
Regarding CodeWarrior - there is a Flash-programmer only "Basic suite", and also you can download full-featured 30-day evaluation version.