Wouldn't recommend it but here is the calculation to get to 50/50 from 30/70. Would be a better idea like chopper suggested to get a 70/30 mix and mix them both together.
You will be diluting down by quite a bit so definitely less strong and less tasty... 40ml added to 100 is 40% of the initial amount.. would make just as a rough statement almost a third weaker overall (ok slightly diff than that but cant be arsed to do the maths here right now)
It's only 16.667ml to make it into a 60VG mix, so that might be a better option only about a 15% reduction in total flavour and nic. I used to run 60VG through my original nautilus all the time with no problems.
He's probably used vapours r us skittles flavour which is on ebay for about £3 for 30ml and came in a couple of day if you have time to order some before you go away.
Thanks wont have time to order any tho but will order some wheni get back im always worried about buying off ebay for things like this as you dont no if its kosher!
I thin my VG for mixing with vodka. You could try that but only use a few drops at a time with caution.Unfortunately you wouldn't be able to accurately gauge pg VG ratios but it would thin it down and give a slightly increased throat hit.