Thank you @Kimi_2 !
I was able to get confirmation from the tax department through support about retroactively applying the new EIN**.** I appreciate your time with this matter. All of the support staff has been great, but this has probably been one of the worst experiences I’ve had with Shopify support (having to contact them 4 times and post in the forums). But, in the end we finally got the help that we needed, and that was due to your guidance.
Hope you have a great day!