A lot of the reading I've done over the years has said that personality disorders tend to get less intense as someone grows older.

And of course it's possible to change. Everyone is changing all the time whether they want to or not!

If by change you mean "completely 'cure'" then no, that is just not possible.

But any individual can work to at least change some of their behaviours. Depending on who they are, and what they're aiming to change, it could take ages or not. It might not necessarily change how someone thinks or feels, but you CAN change behaviours and hopefully that will help with changing thoughts and emotions to a degree!