The proxy issue is a bit of a weird one. I think they will tend to say no a lot of the time due to the need to sell stuff. Or tell you that you can only proxy 1-2 times before having to buy the model if you want it. Also it depends how much of a proxy it is as well. If you are just saying "I want to try my raptors out as warp talons" then I think most will let it go, but if you say you want your terminators to count as Obliterators then they might argue the call.
The strange thing is as far as I know (don't generally go in to my local GW to much) they don't sell magnet kits. These things can be insanely good and they could make a lot of money selling them to people who want to use a Melta 1 game and Plasma the next, or have a Maulerfiend they want as a Forgefiend the next game (examples of 2 things I normally magnet). If a kit has some essential parts required by both things but end up in different places I tend to try to recreate them out of modelling clay or greenstuff or frequently for pipes I can use pipecleaners / straws or various sizes.
Then again my Proxy Heldrake is great and I use it a lot. It is made from an Eldar Crimson Hunter and I have some magnetised bits I add to it to make it chaosy and have feathered wings and the front end gets a lower jaw.
Last edited by mayegelt; 07-05-14 at 10:08 AM.