Centre MacMahon, who starred in Currie's 29-5 win at Edinburgh Accies last weekend to remain top of the Scottish Hydro Premiership, was not included in the initial 25-man squad named earlier this month.
McMahon joins club-mates Ally Hamilton, Mark Cairns, Ross Weston and Richard Snedden while Heriot's hooker Scott Burnett previously played at Currie.
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Hide AdSquad: Fraser Harkness (Selkirk), Fraser Thomson (Melrose), Malcolm Clapperton (Boroughmuir), Jamie Hunter (Ayr), James King (Melrose), Lee Jones (Selkirk), Andrew MacMahon (Currie), Scott Wight (Melrose), Richard Snedden (Currie), Alan Dymock (Heriots), Gregor Wood (Watsonians), Gordon Reid (Ayr), Scott Burnett (Heriots), Alastair Hamilton (Currie), Alan Brown (Dundee), Damien Kelly (Ayr), Scott Sutherland (Ayr), Rory McKay (Hawks), John Dalziel (capt) (Melrose), Mark Cairns (Currie), Paul Burke (Ayr), Ross Weston (Currie).