Yes. If you feel comfortable doing so, you may alter the source code to suit your needs. Please read the license agreement for more specific information regarding altering the code. Note: The source code is 98% unencrypted source with the 2% encrypted portion dealing with licensing. Complete customization can be performed without the need to access the 2% encrypted code.
License Agreement: http://www.turnkeywebtools.com/docs/license_agreement.pdf