I'd assume a lit more changes to be adopted muchquickeras they are shown to be effective under more circumstances. Take positional warfare and cover and concealment for infantry. The uses of techniques previously thought applicable only in sieges (trenches, foxholes, sniping, camouflage, indirect-fire artillery, small-unit ops) were shown to be effective in the field in the Latest Unpleasantness, the Franco-Prussian war and Italian Wars of Unification. Ditto the uselessness of cavalry charges against massed troops. However, because these events were rare and widely spread (and because generals of a certain mould could prove the old ways still worked, they just cost a few ten thousand extra dead) there was no need to apply the lessons in aconsistent manner. In the event of numerous great power wars we would see these changes much earlier. By 1900, the trench stalemate would likely have been broken already by small-unit tactics and independent operations.
As to technology, I think this would depend on the mindset the wars were fought in. MOst of WWI was fought in an almost manic belief that it was about nothing less than national survival, so naturally anything went. THe 19thcentury usualkly took a different attitude in these matters. If you posit that the great power wars change that we can expect chemical warfare, dynamite guns, bombardment of civilian targets, and such lovely inventions as concentration camps, firestorms and forced labor brigades to factor much earlier and much more widely. If not, I'd expect more of a somewhat playful, tinkering approach to military problems that gives us the staples of steampunk fiction (albeit not very effective). The selection process of battle then might even give us working airships and steam tanks...