[Phanx]

I assume the original code read:

local party = oUF:SpawnHeader('oUF_Party', nil, 'custom [grouparty,nogroup:raid][@raid6,noexists,group:raid] show;hide',
--local party = oUF:SpawnHeader('oUF_Party', nil, "solo", "showSolo", true, -- debug
"showParty", cfg.ShowParty,
"showPlayer", true,
"yoffset", -20,
"groupingOrder", "1,2,3,4,5,6,7,8",
"oUF-initialConfigFunction", ([[
self:SetWidth(%d)
self:SetHeight(%d)
]]):format(128, 25))

In which case you just need to add the attribute and value in the list of attributes and values that already exists, not add a new SpawnHeader call in the middle of the list:

local party = oUF:SpawnHeader('oUF_Party', nil, 'custom [grouparty,nogroup:raid][@raid6,noexists,group:raid] show;hide',
--local party = oUF:SpawnHeader('oUF_Party', nil, "solo", "showSolo", true, -- debug
"showParty", cfg.ShowParty,
"showPlayer", true,
"yoffset", -20,
"groupingOrder", "1,2,3,4,5,6,7,8",
"sortMethod", "NAME",
"oUF-initialConfigFunction", ([[
self:SetWidth(%d)
self:SetHeight(%d)
]]):format(128, 25))

As for adding pet frames, that's much more complicated, as many parts of the code would need to be modified to support those units, and new parts would need to be added, and I just don't have any interest in rewriting someone else's addon for you, sorry.