Welcome to the forums! :-)
Yea, the rule is called WYSIWYG (what you see is what you get) It refers to wargear not standard to the model such as the flamer and power sword you mentioned. Really its more for tournement scenes where your opponent needs to be able to see what you have. In casual play, most people wont care as long as you specify what your models should have... unless they are DI#*S!!!
Some solutions to make it easier to move weapons around from model to model are using pins or magnets. Works great for vehicles too! Or if your running, say a razorback, dont even glue on the turret or hatch and just sit it in place. This way you can swap weapons around, or take it off if you want it to be a rhino or suffered a weapon destroyed roll.
Last edited by CE5511; 03-01-12 at 01:25 AM.