Are you closing down your old email address or is it no longer valid? While there is no easy way to update all the companies, for most you can go into your profile and make the changes easily enough. To make it a bit easier, just copy/paste the new address in each. If you haven't or don't want to create a new PayPal account, just link the new address to your existing account.
I don't recall whether having different email addresses for PayPal and for shop notifications is an issue with very many of the MSCs. My browser fills in the basic information for me when registering for a new company, address, email, etc. On one I failed to proofread and didn't realize one of my alternate email addresses ended up in the PayPal field. The MSC communicated with me through my mystery shopping email, but paid through the alternate email. I was able to easily link that email and get the money. It wasn't completely seamless. There was the initial freak out on my part. We though the MSC was going to have to wait 30 days for the payment to be returned then reissued. I finally realized nobody else had the alternate email address since it had been mine for over 15 years
Then it hit me to link it with PayPal and I had the money immediately, LOL.
Equal rights for others does not mean fewer rights for you. It's not pie.
"I prefer someone who burns the flag and then wraps themselves up in the Constitution over someone who burns the Constitution and then wraps themselves up in the flag." -Molly Ivins
Never try to teach a pig to sing. It's a waste of your time and it really annoys the pig.