How to change the property of all parts in a model?

Apple's code is nice but here is a more flexible one (Recursive too!)

function SetProperties(Item,Class,PropName,Value,Recursive)
    if Item and PropName and Class and Value~=nil then
        for _,v in pairs(Item:GetChildren()) do
            if v.ClassName==Class then
                if v[PropName] then
                    pcall(function() v[PropName]=Value end)
                end
                if Recursive then
                    SetProperties(v,PropName,Value,Recursive)
                end
            end
        end
    end
end
SetProperties(PathToModel,"Part","Name","Name of Part",true)

Assume the model is named "Model" and is in workspace, and the property you're looking for is "Property", and the value you want is "Value". Also assume the type of object is a Part

for _,v in pairs(game.Workspace.Model:GetChildren()) do
    if v:IsA("Part") then
        v.Property = Value
    end
end

First line loops through the model making v equal to the child for each child, next checks if the child is the correct type of object, then everything before the end is in the loop that messes with each individual child.

This only works for direct children of the model, by the way, so if there's a model inside the model it won't work.

The second line can also be replaced with any other sort of check, but needs to make sure it only edits the parts you want it to.