I really can't think of a time I have been more excited by a new Strelets set of figures, so I have been trying to gather some information on the Napoleonic Highlanders this is what I have found mainly from the internet and a few books I have, so feel free to disagree, add, correct or confirm anything.
During the Napoleonic Wars in the British Army there were 11 Highland Regiments and they served in Europe, India, the Caribbean, the Americas, South Africa, the far East and numerous other places where the British Empire had an influence.
All the Highland Regiments at least up until 1809 wore the Kilt and Feather Bonnet, after which time some continued wearing the Kilts and others lost their Highland status and changed to wearing regular British infantry uniform in order to appeal to none Highland recruits (Lowland Scots, English and Irish) to help fill the ranks, below I have tried to clarify who wore what and when.
42nd Royal Highlanders Black Watch; were the only highlanders to wear the kilt throughout the Napoleonic Wars and along with the 79th and 92nd were the only three Kilted Highlanders present at Waterloo. http://centjours.mont-saint-jean.com/uniformes_uniteBR.php?uniformes=22&nation=1
79th Cameron Highlanders and 92nd Gordon Highlanders both wore the Kilt for the majority of the Napoleonic Wars except in the Peninsular when after 1809 their worn out kilts were made into tartan Trews before being replaced by grey trousers by the time they appeared at Waterloo they had been resupplied with Kilts.
78th Ross-shire Buffs wore the Kilt for the majority of the Napoleonic Wars and were mainly stationed in South Africa and India, the 2nd battalion did see action during the 100 days whilst on garrison duty at Nieuwpoort in Belgium, however even more intriguing it would seem a detachment of five men (2 officers, a sergeant and 2 Privates) were at Waterloo or Quatre Bras as they were awarded the Waterloo campaign Medal. http://centjours.mont-saint-jean.com/uniformes_uniteBR.php?uniformes=105&nation=1
72nd, 73rd,74th (Argyll),75th and 91st (Argyllshire) lost their Highland status and changed to wearing regular British infantry uniform in 1809 in order to appeal to none highland recruits (Lowland Scots, English and Irish) to help fill the ranks.
Many Highland Officers and Flag Bearers (Ensigns) wore the Kilt up until 1809 unless mounted on horseback in which case they wore Trews or Trousers for practical reasons, after 1809 they all wore Grey trousers.
Bagpipers tended to keep wearing Kilts regardless of whether they lost their Highland status or not.