Cypress.config() inside test does not override "blacklistHosts" value

[CKuB]

Current behavior:

Adding Cypress.config('blacklistHosts', '127.0.0.1:63342') within test does not override global blacklistHosts in cypress.json

Is it a bug or a feature?

Desired behavior:

Adding Cypress.config('blacklistHosts', '127.0.0.1:63342') within test overrides global blacklistHosts in cypress.json

Test code to reproduce

I have no opportunity to add my tests here((((

Versions

Cypress 4.5.0, MacOS 10.14.6, Chrome 81

[jennifer-shehane]

blacklistHosts is not writeable at the time that Cypress.config() is called here. It needs to be set before the browser is opened. We should warn in these circumstances. Duplicate of #6407