Use 'alterable' when something has the ability to change, but hasn't changed yet. The room's layout is alterable depending on our needs.
Pro Tip 2/3
Controlled Modification
'Alterable' usually implies someone has control over the change, rather than it happening randomly. The policy is not fixed; it's an alterable guideline that we can adjust.
Pro Tip 3/3
Not Always Easy
Even if something is 'alterable,' it does not necessarily mean that changing it is easy or simple. The car's design is alterable, but it would require a lot of work and money.