I'd still be trying to keep to a Star Wars style/aesthetic obviously, but I'm worried that a deliberately oversized arm would, in and of itself, be too odd for approval.
Here is the way I always approach anything when it comes to designing my kit:
If this character walked out on screen in a SW movie or TV show, would any part of it seem out of place, or not part of the universe?
Does it seem realistic for the SW aesthetic?
If you got a call from
The Mandalorian's production team looking for an extra, would your kit gel with everything else on the screen?
My 2 credits on this would be; What era are you going for? If you are going Early Crusader or Crusader era (an era with older tech) then it would make sense that it may have to be oversized to a bit for that time period (look up Cay Qel Droma for an example). For modern or Post-Imperial eras, the cybernetics we see are very trim and form fitting, if not disguised to look like the actual limb (Luke, Vader, etc.). So, while you could do it, what would be the purpose?
If a trimmer one was as strong, why need a larger one?
Would it off balance your Mando? How would they get their armor off/on over the oversized limb?
Would their armor have to be modified to accommodate that?
If it was a leg (rather than an arm) would it look out of place?
Is this what a cybernetic physician/droid actually install for this character?
