Hi Adrian,
it is (was) a great step from T2 to T5, so it is not easy to give the "right" answer here.
The least problems you will probably have when you adapt T2 Regs to the T5, because almost all Voices and Effects of the T2 should be in T5. Also the Styles have changed, and some T2 Styles are no longer in T5. But you can use T2 Styles on the T5, of course.
The opposite way (to adapt T5 Regs to the T2) will be more complex, in my view. In many cases, almost everything will have to be changed, because most content of the T5 is NOT available on T2.
Best regards,
Chris