I've done this a few times, and the best advice I can give is to just use a knife and some greenstuff. The suits tend to have circular joints, so it's not too hard to cut around them and reposition the arms/legs. Greenstuff is useful for filling in gaps or fixing details in this case.
Here's an example of something I did. I don't want to steal your thread or anything, so I'll just post a link...
Any knife you use for modelling should do, using small clippers can sometimes be easier to cut with so the joint is loose, then finish it off with the knife. Be careful with the knife though! try not to apply too much pressure because that's when you can slip and end up with a bloody mess. If you're pushing on the knife and it's just not cutting, use the clippers to loosen it up a bit then try again with the knife.
I converted my own battlesuits so they could have varied poses, I found that cutting beneath the knee joint and then reversing the leg and re-attaching it on the other side helped with some of the poses. Example: http://imgur.com/TCY4R.jpg
(not my models btw)
If you look at the battlesuit on the right, you'll see the bottom half of the leg has been reversed. You can also cut at the elbow joints on the arm, then re-attach so that the arm is fully extended which can help improves pose as well. Then just fill in any gaps with greenstuff. Good luck!
I have found that a saw is a million times neater than a knife or clippers if you have one.
Depening on how you want to pose the arm depends on where you cut it. For plain straightening cut it at the "wrist". This means you can pin the arm in a new position with very little green stuffing.
Rotating the arm is a bit different, cut the arm above the elbow, being neat here will pay off though. Here are some pics of 2 suits that are waiting to be painted.
Sorry for the poor pics, I only took these a moment ago to show you.
In general, the right arm is alot easier to re pose because the left arm is slightly more closed so that the wrist and the shoulder actually touch meaning that after they are cut, the edges need to be rebuilt with green stuff like so:
Apart from that I can't stress the importance of pinning your new joints, it saves so many headaches, both in construction and when they inevitably break because you breathed on it.
A friend of mine posed my crisis suit for me. He just hacked one of the legs off at the circular knee joint, positioned it further round and then cleaned up where he'd cut with a craft knife and filled in the gaps with green stuff. I'd imagine the arms work in a similar manner though I'm REALLY new to Warhammer modelling so I dare not try it yet.
A forum community dedicated to Warhammer, Warhammer 40K enthusiasts. Come join the discussion about Warhammer and Wargaming collections, miniatures, tactics, terrain, reviews, accessories, history, displays, models, styles, scales, reviews, accessories, classifieds, and more!