^^ lightening your hair is definitely permanent, though over time it might fade/get brassy/etc, and as it grows out you get roots -- but that's the whole point
where are you from? since it'll technically last a long time and growing out isn't an issue, you could always get it done if you are on a trip somewhere with better hair salons?
lemon juice + salt etc will probably just make your hair a bit lighter or reddish, but should still have an effect...
if you can find out exactly what it is you're allergic to it might help figure out what options you have
have you used peroxide (hydrogen peroxide, the brown bottle stuff from the drugstore) before and been ok? i'm fairly sure a lot of hair bleaches are peroxide based and not necessarily sodium hypochlorite or calcium hypochlorite or those like chlorine bleaches, which is the stuff that "smells" like bleach and we think of as Clorox, etc, and that also makes ME itchy (but no hives) if I use it on my clothes.
i am allergic to nonoxynol-9 which is (haha gross) used as a spermicide in condoms but also shows up in a lot of box hair dyes -- but i've been fine at salons nearly all the time, and also with buying the developer + dye tint separately from a beauty supply myself as opposed to like a box of l'oreal feria or whatever.