Hi!
Backing up a site doesn't cause the site to be modified in any way, so no, that's not a risky process.
Regarding transferring a site back and forth, the only risk is that any data created on the site between creating the dev site and restoring it back to the live site is lost. This means that if you have created an article, or if someone registers on your site, this information will be gone. But this only applies if you backup the live site, restore it to a dev site, do some work, then back it up restore it back to the live site. In all other cases it doesn't apply at all.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!