method 1 (preferred)
you can leave the LEGEIMG.zip to the root of your goldcard and go to boot loader and let it load and you confirm the update. i suggest using the same one that you use for the downgrade.
if, you don't have it download
Legend rooting tools, extract the zip. locate testimage.zip... copy it to your goldcard and rename it to LEGEIMG.zip. (make sure you dont ended up renaming it to LEGEIMG.zip.zip if you know what i mean lol)
method 2 (goldcard not needed)
For the past few days i've been playing around with official RUU. and heres what i've done so far on testing the official RUUs from HTC (link from stickies)... it'll turn your Legend to stock.... even if your on CM7 or any other roms....
But... if you have an HBOOT of less than 1.00... be warn. RUU with Froyo will update it and there's no known method to downgrade. unless you dont care about it and thinks its about time you update it and you have intention on doing the S-OFF...