Hey there Blond Ambition! LOL!
This is always such a challenge, and it always makes me giggle that a level 3 wants to be the complete opposite of what they are! Even so, it is completely possible!!! My best advice is to never let the lightener dry out, keep it moist throughout the entire processing time. As you have the first re touch applied, let it set for approximately 15 mins. then with a fresh formula reapply the retouch again to continue the moisture and also it keeps the hair in the alkaline state. I usually mix the second application with a lesser processing lotion. In Goldwell speak, apply first retouch with Oxycur Platin Ultra and 30 volume, with the second being 20 volume. This usually will "flip" the level 3 in still about a 30 to 40 minute window. Now, the glaze or toner at this point will probably need to be an alkaline glaze, since you are traveling a long way. An acidic glaze is great for the ends, though you need to squash the remaining warmth. Try 20mls 20vol 20mls 10a for 10 to 20 mins for a cool ash, another favorite is 10mls Topchic 9GB 10 mls Topchic 9PV. This will give you a beautiful clean canvas that will not fade back to warm.
Oh and PS, make sure they are retouching no later than every 4 weeks! Let me know your results, though I know you will be happy! Hit me up any time with other questions, or just to say hey! Happy Blonding! j