Users that have already pre-registered as testers in previous PS4 software betas will have access to this new feature "soon".
Sony says PSN name changes will be fully compatible with all PS4 games published after April 1, 2018, and the "large majority of the most played PS4 games" from before then as well.
The blog post added: "During the preview, you will be able to change your online ID as many times as you want".
You will be able to display your old username alongside your new ID in order for friends to recognise you online. However, unlike the previous setting, this option is only available while applying the change and not after. Subsequent changes will cost $9.99 USD / CAD, while members of PlayStation Plus are afforded a hefty 50 percent discount at $4.99 USD/ CAD per change. So I'm anxious that, in a few months, we'll start seeing a flood of posts on the PlayStation forums or subreddit in which users are upset about losing game progress, saves, or trophies because they changed their names. For PS Plus members, changes will cost £3.99 / $4.99. This can not be changed after setting it, so your old ID be forever stained onto your profile if choose to do so. We'll get a list of officially compatible games at some point in the future. This should solve "most" issues. Now, you won't be able to change your name quite yet, but rest assured that it's coming.
Perhaps unsurprisingly, Sony notes that not all games for PS4, PS3, and PS Vita will support PSN ID Change. Sony will provide a list of supported ID change games (again, this is freakish that it doesn't just work universally, and a glimpse into Sony's odd infrastructure). There'll be a short wait after that, with the feature set to officially roll out for all users sometime in early 2019.