hmmm, that's a difficult one to answer! if it's a sub contractor that's installing it they almost certainly will yes for a fee of course,
but if it's one of sky's in house installers, it will depend how much of a jobs worth he is tbh. no there not really allowed to, but some will to earn a bit of cash on the side.
the other thing to mention, is that sky now more often than not just fit quad lnb's so you may not need to pay extra for an lnb and just pay them for the cabling, unless your intending to do that yourself of course