Welcome to the Community, @Sam4! 
Yes, you’ll be able to do that. The feature is not enabled yet, but once it is live, you will be able to opt out of receiving interest via a section in your account’s menu.
As @Dougal1984 mentioned, the interest will be credited to your account automatically at the end of each Business Day and reflected on your periodic Statement.
In the unlikely event Trading 212 or the bank holding your client funds were to go into liquidation, and if there was a failure to safeguard your assets, the value of your funds and assets held with Trading 212 are still protected by the applicable compensation scheme.