I stand corrected on the ability to change a constitution, but I stand by the assertion that changing a Constitution is more difficult than changing laws.
Perhaps how easy or hard it is depends on the constitution in question. Some might be easier to change than others. So yes some specific consitutions could be harder to change whilst others are easier to change.
If it's too easy to change a Constitution, then that Constitution becomes too vulterable to mob rule, or political fads of the day.
It SHOULD be hard, but it should be possible, ideally, when it really matters.