This is going to depend on your ISP - it isn't something that we can definitively say. Likely, if your ISP owns the cable modem, they may not grant you access to do that. Then again, they might. A question for them.
If you are concerned about the security of this device (which is great) or are concerned about the integrity of the ISPs network (or about anything the ISP might do, like inserting ads or messages into http traffic), my advice would be to first ensure there is hardware you own between your devices and the cable modem and to ensure that that hardware has good passwords and is kept up to date - product recommendations are off topic here, but there are some good open source router firmware replacements out there that might be more reliable and secure than factory default ones.
Secondly, don't allow unencrypted traffic to go out over the modem, wherever possible. You can do this either by using https everywhere (this takes work, though there are browser plugins that automatically update to https where available) or by using a VPN (this just moves exit point, though, and requires you to trust the VPN provider - https everywhere is still an excellent idea)