It doesn't necessarily have to increase the gravity...

by General Vagueness , The Vault of Sass, Saturday, August 31, 2013, 12:46 (4100 days ago) @ Xenos

As far as I know, the jjaro tech could only fold mass AWAY, not add it :-p

Just used to my Bungie being hard sci fi.

Technically it could compress the planet which would decrease r which would increase the effects of gravity on the surface of the planet.

You could do that too, but size is another one of those key defining characteristics of a planet like mass, composition, layers, and orbit (though you can still apply what I said in my other post).
If you did a little of both-- add mass and reduce size-- you could have something the size of the planet or moon as it is but with more gravity. If you just added to the outside and squeezed, though, you'd lose all the surface features even more definitely than if you just covered them with added mass. If you could remove the outer layer of the planet, add mass to the inside, and then reapply the top later and squeeze, it would look more like its old self, and even more if you removed the top, added mass, squeezed, and then put the top layer back on.