Is there a way to make this code possibly shorter?

Sure! Just use a while loop. This will keep it going forever,

while true do
    for i = 1, 10 do
        wait(0.01)
        pMenu.loading.ImageTransparency = pMenu.loading.ImageTransparency - .1
    end
    wait(1)
    for i = 1, 10 do
        wait(0.01)
        pMenu.loading.ImageTransparency = pMenu.loading.ImageTransparency + .1
    end
end

To keep it looping a certain amount of times, just create a value and make it increase after each loop.

local LoopBreak = 0
while true do
    if LoopBreak == 5 then --Once the LoopBreak reaches 5, it will break the loop.
        break
    end
    for i = 1, 10 do
        wait(0.01)
        pMenu.loading.ImageTransparency = pMenu.loading.ImageTransparency - .1
    end
    wait(1)
    for i = 1, 10 do
        wait(0.01)
        pMenu.loading.ImageTransparency = pMenu.loading.ImageTransparency + .1
    end
    LoopBreak = LoopBreak + 1 --Increases the value by one everytime it loops.
end