Adding one more to the list for anyone finding this later: Station Renamer Combinator.

Difference from the two above is that you write the name and the signal goes inside it,
anywhere you want, next to your own words and rich text -- "{icon} Unload", "Smelter
{Name} in", "{fluid} pickup". The other ...

Vanilla still can't, but a mod can: Station Renamer Combinator.

For your case, wire the tanks into it and set the name to "{fluid} unload". The stop
renames to the strongest fluid signal on the wire, and because {fluid} is a type filter it
ignores items entirely, so an item renamer on the same wire ...

This is your spec almost exactly, if you'll take a mod doing it: Station Renamer
Combinator. Parameter substitution in the station name, strongest signal wins.

{icon}, {Name}, {name}, {count}, {type} and {quality}, plus the real interrupt wildcards
{item} / {fluid} / {fuel} / {signal}. The ...

Modder here, this is my own mod, so read it as self-promo.

Station Renamer Combinator does what this thread is asking vanilla for. It's a combinator
you wire signals into; you type the station name as a template and the network fills in
the blanks.

{icon} Unload -> [item=iron-plate] Unload ...