Can't a constitution be changed/ammeneded/altered etc... ?
In most cases, not without revolution. The US is different in this regard, in that the methodology to change the Constitution is part of it's design (Amendment process).
But it requires pretty monumental hurdles to be overcome, far beyond quietly changing laws via routine votes.
A cursory search reveals that, besides the United States, the following countries have amended their respective constitutions: Ireland, India, Canada, Australia (in the form of referenda), Russia, Italy, Turkey, Norway, Brazil, and I think I'll just stop looking right there because it's now become increasingly clear that you're probably wrong about this.