when you remove a cover, the pickup is covered in wax. you need to scrape it off. i suppose that's why people recommend adding more wax. not all pups are wax potted. the 490's are not wax potted, they are scatter wound, whatever that means. according to wiki, anyhow. so if you're putting caps on your 490's they'll need to be potted or they'll feed back at higher volumes.
keep in mind that adding the covers will change your tone. my thinking is, since you have to remove the pup from the guitar body to install the cap, why not go a step further and swap in a nicer set.
i know that some people really like the 490s. i am just not one of them.
i have burstbucker pros, and i like them them for heavy rock stuff, and lead work, but not so much for rhythm stuff. i have 57 classics which have alot more clarity and chime, for when i want to play more chords, or cleans. if you don't want to spend the $$ on gibson pups, there's always seymor duncan. they make great pups, and the cost is more reasonable.