Simpson, 22, started his career at Hartlepool before making a £50,000 move to Championship side Preston North End.
More recently, he has enjoyed time in Iceland and Wales, prior to his move to Mount Pleasant.
Meanwhile, returning favourite Macdonald joins the club after being one of several players released by League Two side Hartlepool at the end of last season, having spent the 2021/22 campaign on loan at Whitby Town.
He also enjoyed five years at Halifax Town earlier in his career, but will now link up with the Pitching In NPL Premier Division side.
On his decision to sign, Macdonald said: “Since I left, I’ve always followed the scores and how they’ve been doing.
“I want to help them kick on even more. I know they got promoted last year. They’ve got some good players here, so hopefully we can kick on.”
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