If you are intending to get a Free Pro installation then the Technician SHOULD replace all cables.
Failure to do so, even if you insist on him using existing cables will put him in a very awkward position, should there be a problem within 90 days.
And service calls generated within that 90 day window will result in the original Technician having the cost of that Service Call clawed back from his earnings.
If you were thinking of a self installation, go ahead use the existing cables, if there is an issue after-wards, then there is a 95% chance you will still get a free Service Call and no-one can have anything clawed back, although Express Vu will still deduct the cost of the Service Call from the Installation Company until it is proved that they did not do the installation.