[Fizzlemizz]

local function createEditBox( nomEditBox, frameParent, posX, posY, text, longueur)
        local nomEditBox = CreateFrame("EditBox", tostring( nomEditBox ), frameParent, "InputBoxTemplate")
        nomEditBox:SetPoint("CENTER", posX + decallageX, posY + decallageY)
        nomEditBox:SetText(text)
        nomEditBox:SetFrameStrata("HIGH")
        nomEditBox:SetSize(longueur, 1)
        nomEditBox:SetScript("OnEscapePressed", function(self)
            local frame = frameParent:GetParent()
            local parent = frame:GetParent()
            parent:Hide() 
        end)
        nomEditBox.Label = nomEditBox:CreateFontString(nil , "BORDER", "GameFontNormal")
        nomEditBox.Label:SetJustifyH("RIGHT")
        nomEditBox.Label:SetPoint("TOPRIGHT", nomEditBox, "TOPLEFT", -5)
        return nomEditBox
    end
     
    editBox1 = createEditBox(self, customWeightPanel, 50, 90, "Box1", 250)
    editBox1.Label:SetText("Editbox 1")
    editBox2 = createEditBox(self, customWeightPanel, 50, 60, "Box2", 250)
    editBox2.Label:SetText("Editbox 1")
    editBox3 = createEditBox(self, customWeightPanel, 50, 30, "Box3", 250)
    editBox3.Label:SetText("Editbox 1")

You could set the text in the function rather than after creating the editbox.