I am a big fan of the how the system in the Star Trek Adventures handles older ships by giving them upgrades. I am not a fan of the system and was wondering of their is something similar in the old Icons Star Trek rpg.
I'm not sure quite what you are asking for. But whenever anyone asks about anything to do with starships in the Last Unicorn iteration of Star Trek I point them to the Spacedock rulebook and Starship Recognition Manuals available to download for free at Memory Icon.
The former is a comprehensive guide to designing and modifying starships, the latter is a set of books collecting data and statistics for a huge number of ships across the eras.
For a second there, I was really confused, thinking someone had done a Star Trek game using the supers rules from ICONS.