Halpin and Hickman have both signed on dual registration from Worcester Raiders and Banbury United respectively.
Hickman, who plays as a full-back, started his career at West Brom, before moving on to Coventry City and Bolton Wanderers. He made a couple of EFL Trophy appearances for Coventry, and also made four league appearances for Bolton. He has also played in Ireland for St Patricks Athletic.
Meanwhile, Halpin is a midfielder, and has made 30 appearances this season for Worcester in the Hellenic Premier Division, scoring four goals.
Both players could make their debuts on Saturday at Dereham Town.
Meanwhile, Mills leaves The Yeltz after making 10 appearances. He made his debut in January during a 1-1 draw against Bedworth United.
His final appearance was a 1-0 defeat against Shepshed Dynamo on Saturday.
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