Is an aluminum foil wrap working as a shield in my spliced USB cable?
Aluminium foil can act as decent shield, many cables use coiled foil wraps around conductors for shields. The coiled foil wraps are typically not as good as a braid or solid conductor.
Aluminum's skindepth for 0.1mm goes to almost 1GHz so even a thin foil will conduct high frequencies.
However, on a digital signal, a shield probably isn't going to do much for a few cm of wire.
Also make sure you make a good connection between old and new shield.