Premium stash tab to merchant tab

I found the page to upgrade it and was initially confused why my stash wasn't eligible to be upgraded. Until I read "unable to be used on upgrades to the initial four Stash Tabs on an account."

Is there a way around this, like if I bought another stash tab? Or am I stuck with a premium stash tab that in my opinion is useless. I think it's ridiculous if I have to spend more money to make it eligible, but I also would find it ridiculous that I spent money on something that I can't even use.

Any help would be appreciated. Thanks