Can I switch between wp.com and wp.org installations as my needs change?

Yes, you can absolutely migrate your WordPress.com website to a self-hosted WordPress.org site at any time.

This step-by-step guide outlines the steps to complete the migration process:

https://move.wordpress.com

If you don’t want to tackle the hassle of moving your WordPress website to a new host, they also offer a Guided Transfer service where one of their 'Happiness Engineers' will transfer your site for you.

Hope this helps!