MacOS doesn't give any way to block an association from happening, I'm assuming they're using the same API's under the hood that Duti is using, and the only way you could block that from being accessed is by disabling the Launch services API.

In the next release of Infat, I'm introducing listing the openers from the plist (As you're doing now). If you record these values, then get their set defaults through infat, you could put those into your config and load from you config whenever they're overriden!

Best I got... Shameless promotion