[jeruku]

To clarify, WoW addon code is loaded sequentially and an infinite loop would halt it.
Using an event like LEARNED_SPELL_IN_TAB may help as it fires when a new spell is added/learned.

local frame = CreateFrame('Frame')
frame:SetScript('OnEvent', function(self, event, ...)
    frame[event](self, ...)
end
 
function frame:LEARNED_SPELL_IN_TAB(self, ...)
    local a = IsSpellKnown(72, false)
    local b = IsSpellKnown(73, false)
    local c = IsSpellKnown(74, false)
    local d = IsSpellKnown(75, false)
 
    if a and b and c and d then
        ChangeActionBarPage(2)
    end
end
frame:RegisterEvent("LEARNED_SPELL_IN_TAB")