[1] : The Collaborative International Dictionary of English v.0.48

alterable \al"terable\, a. cf. f. alt'erable.
   capable of being altered.
   1913 webster

         our condition in this world is mutable and uncertain,
         alterable by a thousand accidents.       --rogers.
   1913 webster

[2] : WordNet (r) 2.0

alterable
     adj 1: capable of being changed or altered in some characteristic;
            "alterable clothing"; "alterable conditions of
            employment" ant: unalterable
     2: of a sentence; capable of being changed to one less severe
see also:
unalterable 

Alterable >> A Words
Alterable, definition of term: Alterable
alterable_pag1.html