Yeah, if your EGR cooler is leaking at the changeover flap shaft, like they all end up doing on the BRMs, you'll still need a new cooler to accomplish what you stated.
If you are handy, you can remove the cooler, cut the shaft and flapper out of it completely, weld the end holes shut, reinstall it, and continue with your plan of dynamic tune. However, when you do that, you eliminate the full heat exchange ability of the cooler since that flap is no longer present and only half of the actual EGR flow will pass through it (the rest will just bypass). So it sort of diminishes the reason for having that sort of tune anyway.