Original answer:
Does this work for you?
describe("test the config json", function () {
it("use web security false here", function () {
Cypress.config('chromeWebSecurity',false);
cy.visit("https://www.google.com");
console.log(Cypress.config('chromeWebSecurity'));
});
it("use web security true here", function () {
Cypress.config('chromeWebSecurity',true);
cy.visit("https://www.google.com");
console.log(Cypress.config('chromeWebSecurity'));
});
});
The config is changed as you can see from the console log.

See document here https://docs.cypress.io/guides/references/configuration.html#Cypress-config
Updates:
After I saw DurkoMatKo's comment I managed to find an URL to test this 'chromeWebSecurity' option. It did not work as expected.
I think changing this config might not work during running the same browser as this is more like a browser feature which will determine when start.
In this case what I can think of is only to run Cypress with different configurations.
The cypress doc here shows clear steps to do this.
hope this helps.