If I had some custom lisp routes that I used with ACAD 2009, then 2012...do you think I would need to upgrade, modify or change any of the lisp to work correctly in 2014?
Could a custom lisp that I used in 2012, corrupt, effect performance, screw with other key commands (although with worked in the 2012 software) in 2014 if I didn't upgrade the 2012 lisp?
And if I need to upgrade my 2012 lisps to 2014, how do I it or where can I find the answer?
LISP is generally portable between versions, more so when programmed with version independance in mind. If you are accessing Civil3D or other objects via VLA methods/properties you will likely need to make updates. There is some command-line quirkyness in the past couple of releases which can affect user feedback during long loop operations.
Oh, and watch out for the security features - these can prevent LISPs from being loaded.