Discovered this by a fluke while restocking a vendor. Now this is a little complicated so pay attention. I had both of the ranged arms attached while I was restocking and noticed when I went to the sell item catagory my arms, which were attached to me poped up. So I clicked on one and sold it. Took the arm off of me so I did the other cause I wanted them both off, then cancelled the auction and placed them in my inventory. Later on when I went to shoot something I noticed everything I shot at was out of range all the way to 30 meters. I couldnt figure out what was up. Hit ctl S and there it was. It still registered that I had arms attached, but by using the vendor to remove them it reversed the modifiers of the arm and multiplied it by 2.
For example. The ranged arms I had on gave me +15 range distance -10 melee accuracy and -10 melee defense.
When I took them off at the vendor my mod showed up as -30 range distance +20 melee defence and +20 melee accuracy.
Basically what you have to do is look at the arms you have on and flip the negative and positive mods and multiply by 2.
So I did a little research and most of the arms will benefit the melee professions, but if you have the rez arm and do not care about loosing healing, you can gain ranged mods when you do this.
I did not get a chance to see if you could do this multiple time over and over becuase my toon is ranged and I did not have a rez arm. If it does stack Im sure this could be done at the bazarr in theed and you could run back up and put them back on. If it stacks, you would get +100 melee def and +100 melee accuracy in 5 trips.
But do not worry, the 3 times I have done this it resets when you log out. So if you mess up it will only be for that session.
Now the servers have gone down for pub 18, so I'm hoping this still works cause I didnt want to post this until I confirmed that it worked everytime and was not a 1 time deal.