It isn't trivial, but it isn't hard by any means. All you do are tearing down the console, cleaning the paste off and adding new and reversing process to rebuild. Anybody familiar with computers should be able to do it very easily. Now if you are talking about delidding and replacing on the IHS yeah that is a fair bit more involved. But I only replaced paste on my 2008 model Phat PS3 and did not delid. I got it on eBay in 2018 console only for $60, had every orifice packed with dust bunnies and over a cup and half of it clogged inside. Somebody kept the poor thing on the floor playing from 2008-2018 so 10 full years. System went from 83c idle temps before I tore it down and refurbished paste. Then something miraculous happened, it idled at 53c and never had any issues with it since then. Although might be due to having the 65nm processor so less thermal heat production maybe but all is well and no need to delid for me. I seriously wished I had documented the process, talk about the most satisfying system refurbish. Still got her running perfectly almost 4 years later.
Anyways, that being said. 11 years I would say it is a good time to change it out. I would never even let an older PC go that long without a change. At the minimum I would do every 6 years or so to keep optimal if using an older PC for many years. Console I would say just good rule of thumb to do it every decade. Depends on how much use it gets and stuff too but yeah, good rule of thumb is every decade. By the way, I use MX-4 thermal paste, some of the best on the market.
https://www.amazon.com/ARCTIC-MX-4-2019-Performance-Durability/dp/B07L9BDY3T
Damn seems it is on sale for $6.10 compared to $9.99 so that seems like a great deal to me. They say they have free shipping too.