Great job, Mateus. This is the exact conversion I plan on doing, but with all charging Zvezda figs and 2 flags. I think I'll go with the 1812, pre-guard Pavlovs to avoid the problems you faced. No doubt it was your desire to use the Zvezda flag figure. If memory serves, the Pavlovs carried their old 1798 (?) Tsar Paul flags until they were promoted to the guard in 1813.
Your blog post says that the Italeri Pavlovs come wearing the early 1805-07 uniform, but I beg to differ. They have the later, 1809 issue rectangular backpacks, rather than the cylindrical knapsacks of the early period. But they do wear the early version boots rather than the later gaitered trousers, so it is a bit inconsistent.
Along with 1812 Pavlovs, I've already converted Italeri Pavlovs to be the early Moscow Grenadiers, but headswapping with HaT early Russian infantry figs in a firing line posture, so they have the early boots AND the cylindrical knapsacks. I'll have to photograph them sometime and post that stuff.
Always good to see a good conversion unit. What I like best about them is that they create a completely unique unit of figures, like no others in the world. Bravo.