This is a little more complicated than it sounds like.
Objects have an intrinsic characteristic called mass (yes, I'm being sloppy with the meaning of intrinsic, but that doesn't matter here). A kilogram is a measure of mass.
A pound is not a measure of mass. The unit of mass in imperial measure is called the slug (I'm not kidding about that). A slug is about 14.5 kilograms.
http://en.wikipedia.org/wiki/Slug_%28mass%29
A pound is a measure of weight. Weight is not an intrinsic characteristic. It's a measure of the force due to gravity. The force of gravity on an object of mass m[SUB]1[/SUB] exerted by another object of mass m[SUB]2[/SUB] is
Gm[SUB]1[/SUB]m[SUB]2[/SUB]/r[SUP]2[/SUP].
Where G is Newton's Constant of Universal Gravitation.
This force is not a number, it's a vector (a number with a direction). It points toward the center of the object with mass m[SUB]2[/SUB] (or downward as we usually call it). If you put a scale under the object the scale will measure the downward force.
But suppose your object has another force acting on it (say another gravitational source nearby). Then two force vectors will need to be added together to determine the total force on the object. If the second source is straight up from the first source, it's gravitational attraction will work directly against the initial object's gravitational attraction. If it's in another direction it's gravitational attraction will work partially against the original object's attraction (if it's directly downward, it will add to it).
In any case, the weight measured takes some work to calculate, but regardless the mass will not change (barring excessive speed or other relativistic affect).
ETA: The momentum of the object will be affected by the sum of all forces acting upon it. The actual calculations in a complicated system require some calculus. This is especially true if the two sources of gravity are moving relative to each other.