Easiest way to get promo pricing for an existing customer?

Basically, the title.

I am a super boring user - I am currently on a Dark Star 5Gb Pooled plan for $15/mo and - honestly - this covers all my needs with a good margin - based on the Dashboard, my average data usage is 2Gb / month and voice usage - ~200 min / month.

I do however see that with the Unlimited Started, going with the current promo pricing, just for $1.50/month more, I can get Unlimited data instead, 20Gb hotspot + roaming - just in case I decide to spend a week in Europe this fall.

Not that I need it, it's more like "everyone has it, why can't I have it too" kind of itch...

That said, any proven recipes for making this itch go away LOL?

Do I have to port out to Tello / Visible / anywhere else, potentially for some trial, and then port back to US Mobile? Any specific waiting period or rituals I have to follow?

P.S. And please, don't get me wrong, I'm not bitching here, it's just a similar feeling to when you rent Corolla for $50/day and everyone else comes to the same place and rent shiny Lexus and BMW for $55. I am fine with Corolla and I like it a lot, but...

Thanks!