Can a Block against attacks provided by an Enchanted Item be altered into Armor at will, or does it have to be created that way specifically?
The book is unclear. My inclination is to say that an enchanted item must be fully fleshed out and is only capable of doing the one thing, but that's just me.
What about using 2 of the EI above's Shifts of power to cover your teammates in the Zone? An option, or has to be "built-in"?
Definitely built in. The above is a rules reflection and the change could possibly be abstracted I.E. it's still doing the same thing (protecting one person), but with slightly different rules. Extending it to a zone is changing how the spell actually works.
Similarly, can an "evocationish" attack EI be split to target multiple enemies?
This is kinda similar to the first question. Technically a spray attack is a rules difference not a thematic difference. For example a gout of flame or an assault rifle could attack a single person or be sprayed to hit multiple targets. Thematically they are the same thing, but from a rules perspective they are different.
Again my inclination is to say that the item does one thing. I guess the reason I have for it is that the rules are imbalanced if you allow thematic changes to effect the rules. If I design a EI that casts a single blade of air and you design one that shoots out a blast of electricity, then the GM allows you to spray since it makes sense thematically that isn't terribly fair to me. It encourages players to game that idea, and then you lose some decent ideas, just because the player can't justify a spray attack with it.
Could an Item be Enchanted to provide a specific attack "roll" result? (Example, a tie pin that provides a roll result of +6 to Rapport once a Session)
Yes, kinda. When you do that, what you are doing is using the "Solve improbable or impossible problems" section of thaumaturgy. This allows you to use the spell's power
instead of a skill roll. This gives you a 6 total, not a +6. No rolling dice, no rapport skill, just 6.
There is one example that screws this idea over. Rashid's ointment. Honestly though I have no idea how they do that by RAW.