Yes, that was an aircraft substitution for the Avro to YYZ. That has happened on a few occations. They have also used a A319 from the mainline AC service.
As far as the hammer head is concered thins are going great. They are currently installing the in ground fueling. Once that is finished the jetway from D-9 will be repostioned to is new home out on the hammerhead.
There is now a rumor going that FL doesn't want all four gates as they originally wanted. They may take only two. If this is true one has to wonder what will the other two gates be used for?
UA has already used D-15 and D-16 as overnight hardstands after irrops the other day. UA had aircraft on every UA gate including the closed D9 and D12 as well as D15, 16 and one at the Old International Terminal. Thats the most airplanes UA has had on the ground in PHL, that I have seen since 9-12.
A little less Hooah, and a little more Dooah.