Well, the big thing I would consider adding is a monk or catholic priest with crucifix, maybe mix up the firearms a bit more with some civilian type firearms such as a blunderbuss and flintlock pistol, a knife option would be good so would a pitchfork, maybe a dueling sword from the that era and region (we are talking rag-tag miltia).
A number of folks suggested on a female body on FB, but honestly you could probably do that as separate set onto itself and probably should considering everything from the Sharp's Rifles vibes you have to the alte history and blackpowder fantasy games getting done.
(These Guerillas can also form a basis for 18th/19th century colonists/militia/brigands/pirates/liberatadores in and around the Southern states/Carribean/South America).
Agree on the Shotgun/Blunderbuss weapon option (again see WA rifles extra M1990 Nock gun) ?
Also agree on swapping the short sword out for something more rustic like the Kyber knife found on the WA Afghan box, add old fashioned cutlass someone stole from the Navy/Real Marina?
Optional 'belly' belt ammo box, assorted captured French items such as water gourds, carbines, pistols.
Sombrero heads? Reuse the Hagman/hankerchief and beret heads from the Rifles box ?
Torsos split into upper/lower parts as per the WA rifles set ? - gives you the option to kitbash some into mounted guerillas.
Don Sanchez mounted guerillas come to mind (note he only had 1 squadron kitted out looking like Vistula Lancers).
Mix say 2 of these guerilla sprues with say 4 'regular' Spanish sprues in a box? Then don't need bicorne/top hat heads or short sword on guerilla sprue.
Perhaps look at the way the Perry ACW Union Inf box has been organised?
A mix of 3 sprues :
The bulk of the figures are of the first type, a couple of skirmishers and a single command sprue.
They mould the heads directly onto the torsos and offer a range of hats/toupees for variety.
Remodel both Spanish Regular and Guerrillas offerings on similar lines as a single box?
Main Regular sprue similar to an army builder ~6 figures, marching, hatless with only default bicornes & top hats, the Guerillas get shooting, loading and advancing arms - top hat, bicorne and mix of woolen caps. The command sprue gets the officer bits (split torso for the officer) drummer (do him so he could also be a fifer), standard and NCO bits which could fold back onto the Guerilla sprues.
Ideally should be able to make up an 1808-10 bicorne regular, 1810-11 top hat regular or 1808-1814 guerilla/militia/colonial unit out of the box. Some scope for US 1812 militia too (add tennesee hats)?
@Dennis Horne I think with this skirmishing (firing and fighting) poses are all thats needed with command being a suggested leader, they are guerrillas after all.