Sorry to disappoint Jeff, but this modification, at least in my books, is not good at all…
Besides the obvious electrical difficulties and the need of adding an extra relay you eliminate a major safety feature for the engine.
The Fuel Enrichment Switch, connected in parallel with the vacuum switch (not very trustworthy), does exactly what it says, enriches the mixture after 3/4 of throttle so you don’t burn your pistons at WOT.
Heaving the Kickdown switch to do that job is inadequate, it will activate too late, and you will have to induce kickdown to do that.
And all that for a $1 part?