Silver and nickle mounts are fairly easily distinguishable.. Nickle silver is more gray than the whiter silver mounts. They wear differently. Nickle(nickle silver)is harder than silver(sterling).
Testing would make it easier to distinguish the two.
There is no real way of masking the the engraved design of the mounts without removing the metal and thining it. To fill it with solder would destroy it so that it would not be able to be restored to it's original design.