Our consultant is really hot on Healthy extras and says if you don't have the full amount of a choice then you must count it as a syn. So, for instance, if you only have 3 laughing cow lights cheeses instead of the full 5, then it is not a 'true' HE A and therefore must be counted as 4.5 syns. Healthy extras are there to make sure we are getting enough of the important calcium and fibre and so the full amounts ensure that we are getting the RDA (recommended daily amount)
She says she wasn't actually aware of this until recently, but HQ confirmed it to her.
As for having half of one and half of another, I have known consultants to say that was ok and I know people that do it too but I guess as always, its a case of trial and error!