Loads for me, though does "changing trains" include shack scores? In which case it'll probably be a four figure number! I've left many a station in the hunt for a 'Spoons or an off licence though.
I assume the mention of Mallaig above is either someone track bashing or changing from Sprinter to Jacobite?
Let's think then, though I'm just counting actual changes rather than bailing for shack scores: St. Erth, Par, Plymouth (only left to board a GWR replacement taxi), Tiverton Parkway, Bristol Parkway, Yeovil Junction, Yeovil Pen Mill, Frome, Castle Cary, Bath Spa, Cheltenham Spa, Slough, Maidenhead, Twyford, West Ealing, Didcot Parkway, Banbury (though I've driven past the station), Great Malvern, Newport, Llanelli, Dovey Junction, Machynlleth, Southampton Central, Woking, Havant (only left to board RRBs), Basingtoke, Brockenhurst, Weybridge, Staines, Ascot, Brighton, Chichester (only to board RRB), Barnham (only been outside alighting RRB), Ramsgate, Sittingbourne, Dartford, Lewisham (only left to change onto DLR), Woolwich Arsenal, Three Bridges, Horsham, Haywards Heath, Clapham Junction, Twickenham, Barnes, Farringdon, Kentish Town, St. Albans City, Bedford, Cheshunt, Stansted Airport, Stowmarket, Manningtree, Colchester, Reedham, Welwyn Garden City, Hitchin, Grantham, Retford, Newark North Gate, Lincoln, Barnetby, East Midlands Parkway, Loughborough, Leicester, Kettering, Northampton, Rugby, Coventry, Rugeley Trent Valley, Lichfield Trent Valley, Nuneaton, Stafford, Smethwick Galton Bridge, Stourbridge Junction, Droitwich Spa, Bromsgrove, University, Jewellery Quarter, The Hawthorns, Dorridge, Stratford-upon-Avon, Blackburn, Oxenholme, Kilmarnock, Ayr, Kilwinning, Carstairs, Ardlui, Crianlarich (alighted RRB there though), Dalmuir, Dumbarton Central, Bridge of Orchy, Eaglescliffe, Dunblane, Pitlochry (changed from a Southbound train to head back North to tick Dalwhinnie).