Shirou doesn't gain the knowledge of how to use a weapon when he traces it.
The matter of tracing Noble Phantasms is the fact that Shirou traces the NP's memories and history into its image as well as all the other elements. In other words, he traces all the battles and such its been through.
From that, he is able to basically use a weapon from its own memory, think of it like muscle memory. He has no consciousness of that knowledge, but he instinctively knows how to use it because of the placed memories.
Something like would normally be impossible for a human to imagine, since they WOULD literally have to have all those memories in their conscious mind, but Shirou has a shortcut: Unlimited Blade Works. His Reality Marble stores all that information from just having Shirou observe the weapon.
In other words, no. If he traced Excalibur, and then traced Durandel, he doesn't suddenly have the ability to switch between the two styles of those blades on any old sword (disregarding that Excalibur is more like a broad sword, and Durandel is something of a long sword).
And on a side note, him copying the styles doesn't mean that he's some mirror image of their wielders. His image will never match up perfectly, and that's not even taking in various stats, so it's not like he can fight against them with it, or even get tipped off onto their combat styles.
Moreover, this Shirou wouldn't even have UBW, so it's all moot.
trevelyan1983 said:
Uhm. So the fame boost only applies to the hero? There goes that equalizer, then. It doesn't really matter which sword he traces, then - as long as it's a Shinsengumi Captain's blade, and thus capable of giving him Hirazuki.
It's less 'only applies to Heroes', and more 'this is part of what being a Hero means.' All known Eirei get fame boosts, as it's part of the package, it's just that it would be greater if they were in territory that recognizes them more vividly.
What I mean is, it's not so much that it doesn't necessarily apply to a weapon, but that it needs to be attached to the weapon that's attached to the hero. Fame. You know? Just like how the crystallized mystery of a Noble Phantasm won't do as much out of the hands the of hero that wields it, fame doesn't just 'attach' itself to some smuck that picks up a legendary blade. You can't have one without the other.
There are exceptions, of course (one right there being Shirou and Archer with their Tracing) but I don't really see how something like that would apply in this case.