Past advice - make sure a spawner has been activated & spits out one of it's original mobs (cave spider/skeleton/zombie/etc), THEN with the mob egg in your main hand right click on the spawner to convert it.

For insurance in case some other weirdness causes it to not work (or convert back to it's original mob after spawning one of the new ones), record this process as evidence to present to the mods/admins & request a replacement.

Question - has anything changed? Or is this still sound advice?

still sound advice.