Modifying content-security-policy response headers using declarativeNetRequest and Manifest V3

Question

I am trying to upgrade a Chrome extension to Manifest V3. Our current application makes use of webRequest and webRequestBlocking to modify the content-security-policy directives in order to inject resources from another application into a frame.

Since webRequestBlocking is no longer supported in Manifest V3, I have been trying to utilize declarativeNetRequest to modify the response headers, but keep running into the following errors:

Refused to send form data to 'https://securesite.com' because it violates the following Content Security Policy directive: "form-action 'self' *.example.com".

Refused to frame 'https://securesite.com' because it violates the following Content Security Policy directive: "frame-src 'self' *.example.com".

I have tried to operations "append", "set", and "remove" and have not had success with any. I also do see that the rules are being trigger onRuleMatchedDebug. Any insight would be helpful!

manifest.json

{
 "manifest_version": 3,
 "permissions": [
    "activeTab",
    "webRequest",
    "declarativeNetRequest",
    "browsingData",
    "storage",
    "tabs",
    "scripting"
 ],
 "host_permissions": [
    "http://*/*",
    "https://*/*"
 ],
 "declarative_net_request": {
    "rule_resources": [{
      "id": "csp_rules",
      "enabled": true,
      "path": "cspRules.json"
    }]
 },
 "background": {
    "service_worker": "background.js"
 }
}

cspRules.json

[
  {
    "id": 1,
    "priority": 1,
    "action": {
      "type": "modifyHeaders",
      "responseHeaders": [
        {
          "header": "content-security-policy",
          "operation": "append",
          "value": "script-src https://securesite.com http://localhost:3000; style-src https://secure.alphasights.com http://localhost:3000; img-src https://secure.alphasights.com http://localhost:3000; form-action https://secure.alphasights.com http://localhost:3000; frame-src https://secure.alphasights.com http://localhost:3000; connect-src https://secure.alphasights.com http://localhost:3000"
        }
      ]
    },
    "condition": {
      "urlFilter": "example.com",
      "resourceType": ["main_frame", "sub_frame"]
    }
  }
]