You shouldn't. An user earlier in this topic said his cyclo dsi evo was no longer working on DS-i mode because the cooking mama save patch (the one the DSi evo uses) hax to gain DSi access, was blocked. Remember that 1.4.3U was the one killing most haxxes ie: Sudokuhax, so... don't.
Don't worry, I keep my old black DSi for messing around, those exploits are useless on DSIXL (except for the CycloDSi), I don't really care about my XL, I always keep it up to date, so that's worth trying isn't it?
If it overwrtie the save inside the cart it's not a problem, I can rewrite them.