) Any alteration of an instrument is material which changes the contract of any party thereto in any respect, including any such change in
(a) The number or relations of the parties; or

(b) An incomplete instrument, by completing it otherwise than as authorized; or
(c) The writing as signed, by adding to it or by removing any part of it.

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13 Guam Code Ann. UNIFORM COMMERCIAL CODE
DIV. 3 COMMERCIAL PAPER

(2) As against any person other than a subsequent holder in due course
(a) Alteration by the holder which is both fraudulent and material discharges any party whose contract is thereby changed unless that party assents or is precluded from asserting the defense;
(b) No other alteration discharges any party and the instrument may be enforced according to its original tenor, or as to incomplete instruments according to the authority given.
(3) A subsequent holder in due course may in all cases enforce the instrument according to its original tenor, and when an incomplete instru- ment has been completed, he may enforce it as completed.