After the French army was crushed in 1871 this concern was taken up by the press, especially after the publication of The Battle of Dorking by George Chesney. This was one of the most influential "what if" stories ever written, and narrates the Prussian invasion of southern England, with a final last stand in front of London, and the hills above Dorking. The British forces are destroyed and England falls. What gave the book credibility was not only the apparently invincople successes of the Prussians in Europe, but that the author was a serving officer in the Royal Engineers, and clearly knew what he was talking about.
In real life steps were being taken to redress the balance. By far the most important was the adoption of a breech loading rifle. When James had joined in 1864 he had trained on muzzle loading Enfield rifles, each shot laboriously pushed down the muzzle of the gun. But in December 1866 the regiment started to adopt the Snider Enfield breech loading rifle, in which the cartridge is inserted in a chamber near the rear. Some idea of the difference this makes can be seen from the fact that the rate of fire of trained troops went from 3 shots per minute to 10! The operative word is "trained" - the action is completely different to a musket and took a lot of getting used to, but with war apparently a real possibility, it must have given a lot of confidence to the troops when they saw the difference it was making.
Even better was the Martini Henry. To remove each cartridge from the Snider Enfield each soldier had to take it out by hand, or even turn the rifle upside down and shake vigourously! The Martini Henry, which started to appear in 1871, had a partial expulsion mechanism making it easier to discard spent cartridges.
The heavier fire power available on the battlefield encouraged new thinking on tactics. Initially the French concept of Elan was popular, one write claiming that it was "a very ugly thing to attack against breech loaders, but it has to be done, it is moral force which will prevail". And the concept of a thin red line was still ingrained, most troops were expected to fire standing up on the battlefield, in line. But the 1859 Field Exercises and Evaluations manual recommended troops be trained to attack in column or line, and that all troops receive some training as skirmishers. These would form up in three parts in front of the main firing line, screening it, and could use a looser formation, cover and even lie down prone to fire. The initial skirmish line would have supports 200 yds behind, and a reserve 300yds behind this. As the enemy advances the skirmishers fall back, trying to disrupt the enemy formations before decisive contact with the main body of troops.
Lacking (fortunately!) the chance to test these tactics on a battlefield, the British relied on thought experiments and exercises. The Coldstream aren't mentioned directly in the Battle of Dorking, but three battalions of generic "Guards" are. They travel by train down to Guildford and then march with band playing to the front line. A detachment of skirmishers are sent to hold the railway embankment whilst the bulk line up along the hillside with skirmishers in front. With bearskins and red coats and a mounted officer urging them on they beat back the first Prussian wave, and counter attack, advancing slowly "and firing as they went, but as steady as if on parade" but there are too many Prussians, too much artillery, and they are swept away.
More realistically (possibly?), in 1871 large scale manoeuvres were started at Aldershot, lasting 7 weeks and attempting to actually recreate wartime conditions. The 2nd Coldstream took part as part of a Brigade of Guards. This novel idea (for the British army) was so successful that it was repeated next year on Salisbury plain with the the 1st Coldstream, and then in in 1873 with the 2nd Coldstream at Cannock Chase in Staffordshire. This last was the most realistic yet, exercising transport and medical services as well, but after this large scale manoeuvres were abandoned, as too expensive. Memories were fading.
If you would like to recreate the Battle of Dorking yousrelf I can recommend the boardgame produced by Draken Games at http://swww.wargamevault.com/