MY lesson today: I plugged a tire on my son's Prius (Friday night). Took it to Discount Tire to have them plug/patch it with a mushroom shaped plug/patch. NOPE. Firestone. NOPE!!!
The guy at Firestone, older guy (like me), walked out to the parking lot with me, told me, "NO major chain shop will re-do a previous plug. Period. I agree, it's ridiculous, I've been doing this for 30+ years, what you're asking is totally reasonable, but the perceived liability prevents us from doing it. Take it to a private shop, they'll do it for $10! You won't have a problem."
Did what he advised. Done.