Planish it with the smooth slightly curved face of a hammer ,,don't punch it w/hammer and punch to stretch it out.
Do the hammer work on the back side of the inlay,,not the face if you are concerned with marking up the surface.
But done carefully, you can do the work on the face and not leave any marks behind. You are not hammering straight down as in punching,,but rather with deflecting blows of the hammer face to draw and push the metal where you want it to flow.
Anneal the inlay to more easily work on it.
Lay the inlay on an absolutely smooth, unmarked solid steel surface.
With directional hammer strokes you can move metal in any direction you want to.
Yes you will be ever so slightly thinning the piece as you have to get that metal from somewhere.
But the wide area that is planished and moved to extend an edge or point will thin that area very little.
It's not like taking a small dia punch to the very edge of the problem and pinching it to move it over.