1) Commutability 2) Exchangeability 3) Fungibility 4) Interchangeability 5) Interchangeableness 6) Substitutability 1) Commutability 2) Substitutability 
• (n.) The quality, state, or degree of being replaceable.
Re·place`a·bil'i·ty noun The quality, state, or degree of being replaceable. 
The capability of the software product to be used in place of another specified software product for the same purpose in the same environment. [ISO 9126] See also portability....
[n] - exchangeability by virtue of being replaceable
substitutability noun exchangeability by virtue of being replaceable