Create a seperate media set for your B2D backups.
For that media set you can set the overwrite protection period, eg 2 weeks.
You can also set the append period as well eg 13 days, this will let you append to the media for 13 days, on day 14 you won't be able to append to it, so it will enable you to overwrite this media instead of appending to it.
Then change your backup jobs, you have to point them to use this media set, and also set the backup to "append to media, overwrite if no appendable media is available".
The above is an example of how you could set things up, there are variations you could do, like set the backup jobs to overwrite the media only (not appending).