(I am continuing with the assumption that you are using the Raspberry Pi image.)
Can you do what you are asking? Yes, you certainly can. The OS install for that image is not read-only; you can make modifications to it that persist across reboots.
Should you do what you are asking? I would strongly recommend against it. Unless you know what you are doing, you may run into issues that could affect your DVR server running properly.
If you are truly set on doing this, I recommend moving from the RPi image to a proper computer running Linux. Then use that to run Channels and host your Samba server. (BTW, a simple search for samba time machine backup
gave several relevant sites on the first page of results.)