I've put them both in the alt_name field. Hopefully this resolves the issue.

PS: don't forget to add "PBSO Motorman Highway" to the portion between Lion Country Safari Road and Royal Palm Beach Boulevard, as the article says was also named at the same time (https://www.pbcgov.com/pubInf/Agenda/20250708/3A2.pdf states the limits).

Even in the source you provided:
"The new signs should be installed by September. The names are ceremonial, meaning postal addresses and emergency-response systems will continue to use Southern Boulevard."
Perhaps alt_name works, but I wouldn't call it any more official than Southern Boulevard.

You're not understanding how street names work in Florida. There are green signs at every intersection, ground level and overhead, that read Southern Blvd. On the other hand, when the state legislature assigns a name, it's usually posted on a few special brown ceremonial signs, and the normal green signs are not changed. I'm planning to drive down to West Palm soon to verify that the green signs have not been changed, but if they had we both know there would be a bunch of photos out there showing it, not just those of the brown signs.

Apart from a few likely-AI Facebook posts and a few fake gold signs made for photos, I'm only seeing brown ceremonial name signs: https://www.google.com/search?udm=2&q=trump+blvd+palm+beach

Good catch. Yes, they should, and I will fix it.

Perhaps this was planned in the past, but the extension of CR 435 was never made. I just drove it and it's only signed TO 46. There are no signs indicating CR 435 uses old SR 46.