There's a site I use that checks for membership only on the client side and I use requestly to spoof premium status. Just had to write a simple script like this to modify the response body of the request that gets membership status:
function modifyResponse(args) {
const {method, url, response, responseType, requestHeaders, requestData} = args;
const responseDataParsed = JSON.parse(response);
responseDataParsed.result.user.vip_end = "2030-06-11T14:16:20.000Z";
responseDataParsed.result.user.expire_in = "3573 days, 3 hours";
responseDataParsed.result.user.is_premium = true;
return JSON.stringify(responseDataParsed);
}